How to Instant Apply Preferences in Mozilla Firefox Without Closing Options Window?

Recently we posted about secret “Click and Hold Context Menu” feature found in Mozilla Firefox:

How to Enable Secret “Click and Hold Context Menu” Option in Mozilla Firefox?

Now its turn of another hidden gem. We are going to call this hidden feature “Instant Apply“. This secret feature is related to Options window in Mozilla Firefox.

When you want to change a preference, you open Options window in Firefox which looks like as following:

Default Options Window:

The Options window opens as a dialog box having only Close button and when you select or deselect an option, you need to click on OK button to apply the changes which automatically closes the Options window. That means you can’t see the result of an option change until you close the window by clicking on OK button.

The secret feature “Instant Apply” allows you to instantly apply an option without clicking on OK or any other button. Just select or deselect an option and see the result without closing Options window.

Modified Options Window with Instant Apply Feature Enabled:

As you can see in the above screenshot, after enabling this secret feature, the Options window changes to a standard program window having minimize, maximize and close buttons. OK and Cancel buttons are automatically transformed into a single Close button which can be used to close the window.

It might become very useful when you want to see the effect of an option change quickly without closing Options window.

To enable this secret feature, you can follow these simple 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 instant in the Filter box and look for following boolean key:

3. The entry “browser.preferences.instantApply” 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 instant apply changes in Firefox Options window.

PS: Check out following video showing this secret trick in action:

Also check:

Ultimate Collection of Best “about:config” Tweaks for Mozilla Firefox

[All About Mozilla Firefox] Get Old Things Back, Customize New Things, Reveal Hidden Secret Stuff