Reboot your system. Is the problem still there? ------------- How to crash Firefox (All Systems); Instructions here; https://developer.mozilla.org/en-US/docs/Mozilla/How_to_report_a_hung_Firefox This link has a program that can crash Firefox.

I've already tried that - still shows Firefox as running, but it doesn't appear on the screen.

You rebooted, and Firefox is still running? Did you try the Crash Firefox program? Let’s do a full clean re-install; [http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All languages And Systems] {web link} Save the file. Then '''Close Firefox. ''' Using your file browser, open the '''Programs Folder''' on your computer. '''Windows: ''' C:\Program Files C:\Program Files (x86) '''Mac: ''' Open the ''' "Applications" ''' folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac '''Linux: ''' Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ '''Do Not''' remove the profiles folder. Look for, and rename any '''Mozilla''' or '''Firefox''' program folders by adding '''.old''' to them. Do not rename the '''Mozilla Thunderbird''' folder if there is one. After rebooting the computer, run a registry scanner if you have one. Then run the installer. If all goes well, remove the OLD folders when you are done. +++++++++++++++++++++++++++ If there is a problem, start your '''Computer''' in safe mode and try again. http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia