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

Delete the extensions.* files (e.g. 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/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar ("Find Updates" button in older Firefox versions) to check if there is a compatibility update available.

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

You can check for problems with preferences.
Rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default value.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

++++ UPDATE Reinstalling the All-in-one toolbar also fixed this problem on my friends computer:

1. Go to all-in one toolbar options in sidebar, select the Addons tab and uncheck "Open in sidebar"

2. Restart FF, All-in-one toolbar will have disappeared.

3. Reinstall All-in-one sidebar and Restart FF again

4. Finally return the extensions to sidebar using the FF addons menu option. (go to All-in one toolbar options, select the Addons tab and Check "Open in sidebar" then restart one more.

I hope this works for you too. JB

++++

This happened to me and I followed the instructions above but the problem remained.

Deleting the first group of files required as described prompted the reinstallation of all the addons and I did them all at once (and I do have rather a lot!). Unfortunately the problem remained.

I then deleted the 3 files once more, and also the addons.sqlite file. This time I just reinstalled a few addons at a time to see if it looked like it was going to work. Everything was looking good until I reinstalled the all-in-one sidebar, and then once again it was showing the addons without their icons as disabled (though actually they weren't) and with unresponsive enable and disable buttons.

I now realised the problem was with the all-in-one sidebar so I tried to remove the addons from it using the options (that button seemed to work). I was going to then try and update it but upon restarting FF I discovered it had disappeared. I reinstalled the sidebar and everything was fixed.

So in conclusion, I suggest if you have this problem you try reinstalling the all=in-one sidebar first, although it may not be straightforward to do as you can see from how i did it. I hope this is of help to someone. JB

I reinstalled All-in-One-Sidebar and the problem is solved. Thanks !