NOTE: This article is updated whenever some interesting stuff is found in Nightly build of Mozilla Firefox web browser. So keep checking this page regularly.
Download Links: Nightly | Aurora | UX (latest UI improvements)
UPDATE 58:
"Close Tabs to the Right" option is a useful feature present in Google Chrome web browser which allows users to close all tabs present at the right-side of the selected tab. This option was missing in Mozilla Firefox but now it has been added in the latest Nightly build.

A confirmation dialog box is shown if you click on the option.
Thanks to our reader "Ahmad" for the update...
UPDATE 57:
Mozilla has released first alpha build of upcoming Firefox 24.0 version to the Nightly channel.
UPDATE 56:
The latest Nightly 23.0 build comes with a new bookmark icon in toolbar which lets you access bookmark options as well as allows you to instantly bookmark a page.
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Thanks to our reader "Kyle" for the update...
UPDATE 55:
Recently in following article we told you that Mozilla is going to remove several unnecessary options from Firefox preferences window:
Mozilla to Remove Several Unnecessary Options from Firefox Preferences Window
In latest Nightly build Mozilla has removed the options to enable or disable SSL and TLS protocols. These options were present in "Advanced -> Encryption" tab of Firefox preferences window but now they are no longer present.

UPDATE 54:
Mozilla has removed a few unnecessary options from Firefox 23.0 preferences window. More options will be removed in future builds.
Check out following topic for more details:
Mozilla to Remove Several Unnecessary Options from Firefox Preferences Window
UPDATE 53:
The latest Firefox 22.0 Nightly build comes with a new tab "Services" in Add-ons Manager (about:addons) which allows you to manage social API easily and quickly.

Thanks to our reader "Ahmad" for the update...
UPDATE 52:
Mozilla has released a testing build of its upcoming Metro version of Firefox for Windows 8. The latest Nightly build installs a new Metro version of Firefox in Windows 8 computers. You can launch and test it using the Start Screen in Windows 8.

You can read more about this version at following link:
How to Use Mozilla Firefox Metro Version in Windows 8?
UPDATE 51:
Latest Firefox 21.0 Nightly build comes with new options to customize tracking settings. When you open Nightly preferences, you see 3 new options in "Privacy" tab as shown in following screenshot:
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Thanks to our reader "Ahmad" for the update...
UPDATE 50:
Latest Firefox 21.0 Nightly build adds a new option to the "New Tab" page which allows you to restore removed thumbnails to the page. Whenever you remove a thumbnail from new tab page, Firefox shows 2 new options: Undo and Restore all.
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You can restore the most recently removed thumbnail by clicking on "Undo" option. If you want to restore all removed thumbnails, click on "Restore All" option.
Thanks to our reader "Ahmad" for the update...
UPDATE 49:
Latest Firefox 21.0 Nightly build comes with a new tab "Data Choices" in Options window which allows you to customize privacy settings such as:
- Enable or disable telemetry
- Enable or disable Firefox health report
- Enable or disable crash reporter

Mozilla has moved these options from "General" tab to this new tab. Thanks to our reader "a" for notifying us about this feature...
UPDATE 48:
With the release of new Firefox 18.0 stable version, Mozilla has released first alpha build of upcoming Firefox 21.0 version to the Nightly channel.
This new build features a new animation in download complete notification. When you download a file from Internet and the download completes, Firefox shows a new animation for the download manager icon present in the toolbar as shown in following image:

We would also like to tell that Mozilla has replaced the old download manager window with a new downloads section which is shown using the built-in Library which also shows History and Bookmarks.
Thanks to our reader "a" for letting us know about the new animation...
UPDATE 47:
When you open Firefox in private browsing mode, it overwrites the existing window with the new private browsing window and you lose all the tabs which you were working on. But the latest Nightly build fixes this issue.
The current Firefox 20.0 Alpha build opens the private browsing session in a new window instead of overwriting your running session. So now you can have both normal session as well as private browsing session running at same time. Good move Mozilla...
UPDATE 46:
Mozilla Firefox 20.0 Alpha 1 build has been released and available for download. If you are already using nightly build, it'll automatically update it otherwise you can download it using the link mentioned at the top.
UPDATE 45:
The latest Alpha build of Mozilla Firefox 18.0 version also comes with a Metro version of Firefox specially designed for Windows 8 Start Screen.

If you are facing problems with Firefox Metro version in Windows 8, check out following article:
How to Use Mozilla Firefox Metro Version in Windows 8? Fix Metro App Launching Desktop Version
UPDATE 44:
Mozilla has released first Alpha build of Firefox 18.0. The most noticeable change in this new build is the come back of good old Download Manager. Mozilla has removed the new download manager and replaced it with the old classic download manager window.
Thanks to our reader "Bilal Haider" for the update...
UPDATE 43:
Mozilla has updated the "New Tab" page in the latest Nightly 17.0 build. Now a new "preload" function has been introduced which makes the "New Tab" page faster by preloading it in the background.
Currently the feature is under testing and users will need to manually enable it. To enable preload feature:
1. Open Firefox and type about:config in the addressbar and press Enter. It'll confirm, click on I'll be careful, I promise! button.
2. Now type preload in the Filter box and look for following boolean key:
browser.newtab.preload
3. The entry "browser.newtab.preload" would be set to false. Double-click on it or right-click on it and select "Toggle". It'll set its value to true.

4. That's it. It'll immediately enable preload function for "New Tab" page and it'll load much faster than before.
UPDATE 42:
Mozilla Firefox 17.0 Alpha 1 build has been released and available for download. If you are already using nightly build, it'll automatically update it otherwise you can download it using the link mentioned at the top.
Thanks to our reader "Bilal Haider" for the quick update...
UPDATE 41:
Mozilla Firefox 16.0 Alpha 1 build has been released and available for download. If you are already using nightly build, it'll automatically update it otherwise you can download it using the link mentioned at the top.
UPDATE 40:
Mozilla has made 2 noticeable changes in latest Firefox 15.0 nightly build.
First change is the removal of "Tabs on Top" option. Now you no longer get this option when you right-click on toolbar or select "Toolbars" menu in Menubar. So you'll have to keep the tab bar on top even if you don't like it.
Second change is the re-allocation of "Don't load tabs until selected" option in Firefox Preferences window. In previous versions of Firefox, this option was present in "General" tab of Preferences window but now it has been moved to "Tabs" tab so that all settings related to tabs are present in a single place.
PS: If you are using the Nightly build and want to get tabs on bottom, you can do that using an easy about:config trick:
How to Put Tabs Back on Bottom in Mozilla Firefox?
Thanks to our reader "TheAslan" for sharing this trick...
UPDATE 39:
Finally Mozilla has finalized the "Silent Background Update" feature in Firefox. The latest Firefox 15.0 nightly build comes with this new feature enabled. Now when you install an update in Firefox and restarts it to apply the update, Firefox no longer takes too much time to install the update and no longer shows any screen such as "Installing update...". Now the update is installed in background while you are using Firefox.
UPDATE 38:
Latest Firefox 15.0 Nightly build comes with new InContent Preferences feature which shows Firefox Preferences as web page in separate tab. Check out following topic for more info with screenshots:
How to Enable New InContent Preferences Feature in Mozilla Firefox Nightly Build?
UPDATE 37:
Mozilla Firefox 15.0 Alpha 1 build has been released and available for download. If you are already using nightly build, it'll automatically update it otherwise you can download it using the link mentioned at the top.
Thanks to our reader "TheAslan" for the update...
UPDATE 36:
Latest Firefox 14.0 Nightly build comes with a new simple website security certificate icon in addressbar as shown in following screenshot:
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Thanks to our reader "Kyle" for the update...
UPDATE 35:
Latest Firefox 14.0 Nightly build comes with new re-designed "Download Manager". Now when a download starts, a new "Downloads" icon appears in Navigation toolbar which shows progress of download as shown in following screenshot:

Alternatively you can access the download manager using "Ctrl+J" keyboard shortcut.
Thanks to AskVG reader "Ahmad" for the update...
PS: If you don't like this new download manager and want to switch back to old one, you can use following steps:
1. Open Firefox and type about:config in the addressbar and press Enter. It'll confirm, click on I'll be careful, I promise! button.
2. Now type ToolkitUI in the Filter box and look for following boolean key:
browser.download.useToolkitUI
3. The entry "browser.download.useToolkitUI" would be set to false. Double-click on it or right-click on it and select "Toggle". It'll set its value to true.
4. That's it. Now you'll be able to enjoy the classic download manager in a separate window instead of the new one.
UPDATE 34:
As mentioned in UPDATE 22, recently Mozilla re-designed built-in image viewer in Firefox and put a dark background when you directly view an image.
Now in the latest Firefox 14.0 Nightly build, Mozilla has again re-designed the image viewer and replaced dark background with a new textured background as shown in following screenshot:

What do you think about this change? Looking better?
UPDATE 33:
The latest Firefox 14.0 nightly build comes with new Script Debugger which is disabled by default. You can enable it using following steps:
1. Open Firefox and type about:config in the addressbar and press Enter. It'll confirm, click on I'll be careful, I promise! button.
2. Now type debugger in the Filter box and look for following boolean key:
devtools.debugger.enabled
3. The entry "devtools.debugger.enabled" would be set to false. Double-click on it or right-click on it and select "Toggle". It'll set its value to true.
4. That's it. Now you can access this new Script Debugger using "Web Developer" menu or using "Ctrl+Shift+S" hotkey.

Thanks to our reader "Carbonize" for this info...
UPDATE 32:
The latest Firefox 14.0 nightly build comes with built-in PDF reader. By default its disabled, but you can enable it using following method:
1. Open about:config and type pdfjs in the Filter box and look for following boolean key:
pdfjs.disabled
2. The entry "pdfjs.disabled" would be set to true. Double-click on it or right-click on it and select "Toggle". It'll set its value to false.
3. That's it. Now whenever you'll visit a webpage containing a pdf file, Firefox will open it in its own built-in PDF reader.
This built-in PDF reader uses HTML5 to display PDF files directly in Firefox browser.
Thanks to our reader "Carbonize" for the update...
UPDATE 31:
We told you yesterday that Mozilla is working on a new homepage design and the good news is that the new homepage has been put in the latest nightly 14.0 alpha build.
Following is a preview of this new homepage in action:

The new homepage is very useful and provides quick access to Bookmarks Manager, History Manager, Settings, Add-ons Manager, Downloads Manager and Sync. It also contains Google search box as usual.
Thanks to our reader "Ahmad" for the update...
UPDATE 30:
Mozilla has added a new "Reset to Default State" button in latest nightly build which can be used to restore Firefox to factory settings.
Read more info at following link:
Mozilla to Add "Reset to Default State" Button to Firefox Browser
UPDATE 29:
Mozilla has once again redesigned "New Tab" page in the latest nightly build of Firefox 14.0. Now "New Tab" page looks far better compared to the previous one mentioned in Update 27.
The background color has been changed, also the page title doesn't overlap the website thumbnail. Its shown below the thumbnail which makes the whole "New Tab" page looking cleaner.
Following is a screenshot of this redesigned "New Tab" page in action:

Thanks to our reader "darkprop" for the update...
UPDATE 28:
Mozilla has added a new secret "about:compartments" page in latest nightly build of Firefox 13.0 version. You can access this secret page by just typing about:compartments in Firefox addressbar and press Enter.

This new page shows a list of all live JS compartments. If you don't know, compartments are little segments of memory which is used by JavaScripts in Mozilla Firefox. Mozilla's idea behind adding this new page was to make detection of zombie compartments as simple as possible. Zombie compartments are a kind of memory leak. In previous versions, you had to use about:memory page to find out zombie compartments which was a little bit complicated but now addition of this new about:compartments page makes it easier.
This page shows all running websites compartments separate from system compartments.
It also contains a "More verbose" link which can be used to show truncated URLs in full.
UPDATE 27:
The latest Mozilla Firefox 13.0 Alpha build comes with redesigned "New Tab" page enabled by default. Recently the new tab page appeared in an alpha build but Mozilla removed it from later builds. But now the new tab page is back.

Thanks to our reader "TheAslan" for the update...
NOTE: Previous updates have been removed to reduce database overhead.
PS: If any of your favorite extensions is not working in this nightly build, you can use instructions given in following topic:
How to Fix Broken Incompatible Extensions in Firefox, Make Them Compatible With Newer Versions
Posted by: Vishal Gupta | Categories: Mozilla Firefox
Ahmad
Firefox in today's nightly added option to undo removed New Tab Page thumbnail and also option to reset it.
Ahmad
As per specification of DNT (Do Not Track) header , Firefox Nightly got two more options in Privacy tab of Options.
Ahmad
This change happened long back I forget to share with you, so sharing now, Per Window Private browsing got new Menu button for Private Window.
New FF Menu Button when in private window.
Ahmad
Two changes landed in Firefox Nightly which IMO should be mentioned.
Firefox dev turn on WMF (Windows Media Foundation) backend for Windows 7+ which means using system wide codec, Firefox can play now even H.264 codec and MP3 etc.
Second is being nearing Australis theme, Firefox changed text appear in Location bar to indicate that it can also search as well.
TheAslan
Firefox Nightly supports H.264 and MP3 by default for now.
Kyle
latest Nightly update includes a "Nightly seems slow... to... start." notification bar on bottom. Included in the option includes two buttons:
- "Learn How to Speed It Up"
- "Don't tell me again"
only appears when Firefox detects slow performance/loading rate on your system.
imo Firefox appears to be copying off Internet Explorer 9 [or 10+]'s notification.
Kyle
^^lol oops, sry, a lot of bad english grammar
Max Tsukino
Awesome update and it looks great as a Metro app... but if you are using OblyTile, everytime you use the Metro view it "resets" all the icons you made...
Kyle
Nightly 22 released.
Carbonize
Well we might be on a fast release schedule but the road map is looking a little empty - wiki.mozilla.org/Features/Release_Tracking
TheAslan
Firefox 22 will block 3rd-party cookies by default, but it's just a rumor =)
Ahmad
Firefox added new "Services" option in about:addons to manage Social API.
Carbonize
God knows why though given after all this time we still only have Facebook using it.
Someone
The way services integration is done in Firefox is right. :)
Kyle
latest Nightly update includes a huge URL address bar.
Kyle
^^currently this only works if the search engine is set to 'Google'.
VG
^^ I have Google set as default and using latest Nightly, still I didnt notice any change in addressbar.
TheAslan
Mozilla Firefox Nightly 23.0a1 released.
Ahmad
Services in about:addons got new icon and also added option for uninstallation of services.
Ahmad
Today's Nightly removed several options from Security tabs like automatically download images and enable javascript from options>Security.
You can read about these changes blogpost on limi.net
VG
^^ That's sad. I personally use those options sometimes when I work in a cafe or somewhere else where I get worst Internet speed. These options help in loading pages faster.
SoRiNuS
I don“t know why but my firefox (no addons installed) doesnt have that big round back-forwrd button. Any ideas?
VG
^^ Open toolbar customization window and make sure "Use small icons" option is unchecked.
Carbonize
When did they change the homepage so that the search actually used whatever search engine you have selected in the search box?
Kyle
latest Nightly has a new, redesigned bookmark icon
Kyle
^^the new bookmark icon also allows for a easy one-click bookmark.
carbonize
Except we used to have one-click bookmarking anyway via the star in the URL bar.
Ahmad
Added new Click to enable form on Plugins in about:addons (Plugins) section..
Carbonize
Release Tracker has finally got something on it for the latest nightly. Looks like 24 will be getting the new look tab strip as well as a redesigned menu panel that will be relocated to the right. In fact together it will look remarkably like Chrome :|
wiki.mozilla.org/Features/Release_Tracking
fadlycms
In the last UX build,there a new menu button
It's just like Chrome menu,but in UX there have a big icons in there
This is the screenshot:
imageshack.us/photo/my-images/24/ss1mk.png/
And when i click customize,it will be looks like this:
imageshack.us/photo/my-images/42/ss2ym.png/
sorry for my bad english
Carbonize
@fadlycms - wiki.mozilla.org/Features/Desktop/Panel_Menu
TheAslan
How to enable Hardware accelerated H.264 playback in Firefox:
1. about:config
2. Then search this line:
media.windows-media-foundation.use-dxva
3. Set its value to True
4. Done
Carbonize
@TheAslan I just checked and it is set to true by default apparently.
Ahmad
Firefox 24 got new option in tab context menu, we get option to "Close all Tabs to the right", bug 866880.