It is possible that Firefox crashed and tried to recover automatically.

If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix:

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the IDs of the submitted crash reports on the about:crashes page.

• You can open the about:crashes page via the location bar, like you open a website, or open the crash reports page via "Help > Troubleshooting Information".

See:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter
• https://support.mozilla.org/kb/Mozilla+Crash+Reporter

See also:

• https://support.mozilla.org/kb/Firefox+crashes

Did Firefox offer to do a reset?

Do you have an "Old Firefox Data" folder on the desktop?

When you reset Firefox then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data) is automatically imported and the current profile folder will be moved to the desktop to an "Old Firefox Data" folder.
Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone.

It is possible to recover more data from the old profile, but be cautious not to copy corrupted files to avoid carrying over the problem.

• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

No crash reports, I didn't get the option and there's no folder on my desktop either :/

Do you still have the extensions folder in the current profile folder?

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

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

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 compatibibility.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 of the Search Bar to check if there is a compatibibility update available.

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

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

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