Please check the "Firefox crashes when I start it" help page to see if your issue is addressed there:

https://support.mozilla.com/en-US/kb/latest-firefox-issues

Well, I tried the download the page suggested, and tried opening in safe mode by holding down the shift. It still will not open. Just don't understand. It has always worked fine until tonight.

Right-click on your Windows Taskbar and select Start Task Manager. Look in Task Manager for processes running that are Firefox-related, such as Firefox.exe or plugin-container.exe. If you see either of those, right-click each of them and select "End process". Then try again to start Firefox in Diagnose Firefox issues using Troubleshoot Mode.

• If Firefox will start in Safe Mode, select the option you are presented with to disable your add-ons and plug-ins and restart Firefox normally. You likely have a plug-in, add-on, or a combination of two or more that is causing the problem. Because Firefox allows users to customize endlessly, sometimes there can be conflicts between customized items. From the Firefox menu bar, go to
  
  Tools -> Add-ons
  
  then re-enable them one by one, restarting Firefox after each and testing after each one to see which one or combination of two or more is causing the problem.
  
  
• If Firefox will not start in Safe Mode, make sure you again check Task Manager and end any running instances, then uninstall Firefox and download a fresh copy from mozilla.org/firefox using another browser temporarily. Re-install Firefox (see: How to install Firefox on Windows for more help ) and try running Firefox again.

Please report back your progress.

Task manager says it is running in safe mode. However, it is not opening where I can see the browser. It apparently is running in the background somewhere, but never opening the browser where I can see it. I have uninstalled and installed a new copy at least 4 times and still will not work. Nothing on "crashing on start up" is helping me either. Unbelievable and frustrating. Does Firefox have a phone number you can call for support?

When you started Firefox in Diagnose Firefox issues using Troubleshoot Mode, you did use Firefox safe mode and not Windows safe mode, right? Sorry, but just to be clear.

Please have a look at the help article: Troubleshoot Firefox crashes (closing or quitting unexpectedly) and report back your progress.

Also have a look at the article Profile Manager - Create, remove or switch Firefox profiles

Yes, I started it in Firefox safe mode. I had to do it while holding down the shift key and clicking on the Firefox icon. The browser never opens on my laptop screen. It wouldn't even open the browser. Crazy!

When you uninstalled Firefox, did you also delete the Firefox directory in your program folder?

I went into program file (x86), then Mozilla Firefox file, then opened the uninstall file. I clicked on uninstall and it removed Firefox. I restarted and then installed from the Firefox website.

Things you may have already done but need to make sure of:

• You need to delete the entire Firefox program folder before re-installing when you're having crashes like this.

• You also need to install as an administrator in Windows.

• You have some old plug-ins showing in your troubleshooting report, which are probably in your c:\program files (x86)\extensions folder and should be deleted when you delete your program folder before re-installing

You should look for updates to your video driver, both from Windows update and from the manufacturer's site. (Have a peek at another thread Firefox 8 memory leak for which I wrote a mini-guide.)

Please report back on your progress.

OK, let me make sure I understand. I need to uninstall, then go into my program files and delete the entire Firefox folder. Then re-install as windows administrator. Just confirming.

Yes, delete the Firefox program folder after uninstalling, then reinstall as administrator.

That was the solution! THANKS SO MUCH! Back up and running!