UPDATE: New version of Firefox has been released which automatically fixes the issue so no extra add-on is required.
Many Firefox users are facing a weird issue after updating their web browser to recently released 7.0 version. All or some of their installed add-ons disappeared after updating to Firefox 7.0 version.
Mozilla has acknowledged this bug and released an add-on to fix the issue. According to Mozilla, these hidden add-ons and user data are still intact and haven't actually been removed. Mozilla paused new updates to Firefox to minimize the potential impact on users and will soon release an update to fix this issue and ensure all your add-ons are visible and usable.
If you are also facing this problem and don't want to wait for the new updated version, here is a working solution for you:
Simply download the official "Add-on Recovery Tool" released by Mozilla which will recover the hidden add-ons.
After installation, you'll need to restart Firefox to complete the recovery process. Once Firefox restarts, you'll get your add-ons back.