What Add-ons (extensions) do you have installed?

This issue can be caused by one of the other extensions that isn't working properly.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.json, extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled or not compatible extensions in "Firefox menu button/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.json file.

Hi. I only had AddBlock Plus as my only extension when this started. Now I have 0 extensions, and whenever I install one, it disappears when Firefox is restarted. It happens with any extension.

I've already tried deleting extensions.json, extensions.sqlite, extensions.ini, compatibility.ini and addons.json files, with no luck.

I don't see any disabled or not compatible extensions in "Firefox menu button/Tools > Add-ons > Extensions", when I restart Firefox that window is empty.

Another strange behavior I notice when I restart Firefox after installing an addon (to see if it remains installed) is that the firefox search bar stops working, and becomes non-responsive.

Thanks for your help.

Can you check the extensions folder in the Firefox profile folder to see if the extensions files are still there or that they are gone as well and that you still use the same profile folder?

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

The extensions files are deleted as soon as I restart firefox, and the "extensions" folder is empty after that. The "extensions-data" folder is not affected, after restarting I still see ublock0.sqlite there.

There is only one profile folder, and is the one I'm using.

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

No luck. I followed the steps detailed in the link, created a new profile, started Firefox with it, installed an extension, restarted firefox, and the addon disappeared (it was deleted from the extensions folder under the new profile tree)

Sounds that you have some very intrusive software running if it clears out the entire extensions folder.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10