Make sure your not in safemode... Troubleshoot your Addons *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I'm not in safe mode.

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) 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 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 try to delete the addons.sqlite file. Which security software (firewall, anti-virus) do you have? Some security software has virtualization or sandbox features that may cause problems by protecting and restoring files in the Firefox profile folder. ----- There are other things that need your attention. Your system details list shows that you have two Flash plugins installed: # Shockwave Flash 11.7 r700 # Shockwave Flash 11.6 r602 You should remove the older Flash 11.6 version See "Manually uninstalling a plugin": *https://support.mozilla.org/kb/Troubleshooting+plugins