Are you using the same Firefox Profile Folder for both those versions?

If you do then you should create separate profiles for each of them because not all files may use the same format version.

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox

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

Delete the files extensions.* (e.g. extensions.sqlite, extensions.ini, extensions.cache) 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, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to check if there is a compatibility update available.

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

hello, please try to reset firefox and see if this solves the issue. there are also very outdated plugins on your computer that will leave you vulnerable whenever you browse the web - please update them as soon as possible: https://www.mozilla.org/plugincheck/

Flash 10.3 is still being maintained with security updates (flash-plugin-10.3.183.43), but your Java plugin (6U22) is seriously outdated.

• http://www.adobe.com/products/flashplayer/distribution3.html

Check these settings in about:config.

If set to false then you will not be able to access the firefox addon manager from Tools->Add-ons. You will still be able to access it from about:addons. extensions.checkUpdateSecurity

If set to false then you will get an annoying warning message. extensions.checkCompatibility

Thanks for all of the replies,

I am using different profile folders for each version. Will deleting my file extensions in the profile folder reset my extensions/add-ons?

Also, I am unable to find "extensions.checkUpdateSecurity" in about:config but I can still access my addons from about:addons, just not the menu.

Do you have TabMix Plus installed?

If so, install the latest development version of TMP.
http://tmp.garyr.net/forum/viewtopic.php?f=3&t=15740

Thanks, that worked. Updated Tab Mix Plus and it's all good.

I still having this same problem installing aurora. When it says click 'ok" the installation just stops.