Hi John.

Please try to restart your computer first. Than try if Firefox can start in safe mode. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). You can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If Firefox starts in Safe Mode correctly, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Thank you for your suggestion! Sadly, Firefox will not be visible when I try to start in safe mode as well. The program is running in task manager, but the browser is not visible, and there is not even any window or prompt telling about safe mode. It is just ... nothing.

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json or Localstore.rdf file.

Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

Thank you for your suggestion! Sadly, I did not work. I found the files and deleted them, but Firefox is still as dead as it was.

Hi. You can try to fix this with next steps: 1. Launch a FF with profile manager. You can launch from command line with firefox.exe -p or with changes in shortcut. 2. Create a new profile. I think FF will launch without any problem. Close it. 3. Remove all files from new profile and copy files from old profile to new one. 4. Launch FF with new profile (but actually where are will be all your data).

Please, confirm if this steps work for you.

Thanks for your suggestion. alverus. I tried to launch the profile manager through command line, but the FF-window did not even open ... It is just like as Firefox has been totally banned from life on this machine.

And as before: Firefox is visible in running processes, but that's all.

First, reboot the computer. Then try;

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia