Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

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

Also check for "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions

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

See:

• Basic Troubleshooting: Make a new profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)

See:

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

Tried, but it still won't work. It also crashed when I tried updating add-ons from safe mode.

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

See:

• Basic Troubleshooting: Make a new profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)

See:

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

nope, still nothing.

anyone?

Firefox Crashes

https://support.mozilla.com/en-US/kb/Firefox%20crashes

Check and tell if its working.

Well now that I disabled the automatic add-on updates, the recent crashes had nothing to do with the issue (and when I click on the crash ID I get a "the requested page could not be found." page anyways).

I tried updating my add-ons again, and Firefox didn't crash; it just froze, and wouldn't respond (so I ended the task manually). Tried this: https://support.mozilla.com/en-US/kb/Firefox%20hangs and https://support.mozilla.com/en-US/kb/Troubleshooting%20plugins but the problem is still here.

User Agent longer than 128 characters

https://support.mozilla.com/en-US/kb/Firefox%20crashes%20when%20trying%20to%20download%20a%20file#w_user-agent-longer-than-128-characters

Check and tell if its working.

"reset" is greyed out, can't click it :/

-> In the Location bar, type about:config and press Enter.

The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!, to continue to the about:config page.

-> In the Filter box, enter the following: general.useragent. This will show only the preferences that contain the text general.useragent.

-> For each of these preferences that begin with general.useragent, right-click on the preference and select Reset. This will return your user agent to the Firefox default.

Copy the above lines on a Notepad or Word file -> Close all Firefox Windows and Tabs Except 1 Blank Page Tap -> perform the about:config procedure in the Blank Page tab

OR try following these steps after opening Firefox in Safe Mode

Check and tell if its working.

If reset is grayed then that means that the pref already has a default value.

Did you try the new profile without any extensions installed, i.e. you disabled all extensions that may have been added by other software on your computer?

Also check the settings in the firewall for the Firefox program and the updater.exe program and the plugin-container.exe process.

Thanks cor-el & mha007! :) Here's what I did: 1. Backed up everything with MozBackup. 2. Created a new profile. 3. Restored everything in the new profile. 4. Everything works fine now.

Nevermind, it worked for a few hours and now the problem is back.

i guess you should Disable or Remove the faulty/unuseful add-ons

Uninstalling Add-ons

https://support.mozilla.com/en-US/kb/Uninstalling%20add-ons

Check and tell if its working.

Well I don't really know which add-ons are faulty. I removed 5 of them that I didn't really need, problem still here :/

...mmmh I tried right clicking and updating each add-on individually, and it seems to work for all fo them except HTTPSEverywhere. So that's probably the faulty addon :D

yeah that add-on has been reported as causing problem in Firefox. Uninstall it.

Uninstall an Add-on

• https://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on

Check and tell if its working.

Fix'd - the add-on caused the problems.