Try emptying your Windows User temporary files (not IE temporary files -- use the Windows disk cleanup program if you can't find your temporary folder), and then reboot again. Firefox does not require multiple reboots.

Thanks for the suggestion but I ran disk cleanup and it didn't help--still can't open Firefox or uninstall it. The only other info is that I updated Roboform at the same time as Firefox--because the new version of Roboform is supposed to work with later versions of Firefox.

Can you start Firefox in safe mode? If so, then RoboForm or another add-on may be the problem.

• First, try uninstalling RoboForm (you can re-install from a fresh download later.)

• If that works, then reinstall RoboForm and try again. If the problem comes back, it's probably a messed up RoboForm installation.

• Also, try disabling all your add-ons, then restart the browser. Test the issue with all add-ons disabled. If the problem goes away, then it's one of your add-ons. To find out which one, enable each add-on, one at a time, restart the browser after each and try loading a page that causes the problem. You should be able to methodically narrow it down that way.

Thanks--will try after I figure out how to boot in Safe Mode--instructions say to press and hold F8 key but that doesn't work. Also not sure how I can disable add-ons if I can't get Firefox started in the first place. But I do appreciate the suggestions--have been using Firefox ever since Netscape.

sctl is saying to start Firefox in Safe Mode; F8 is for Windows Safe Mode.

Hold your Shift Key down as you double click on your desktop Firefox icon and continue. This disables your extensions but not your plug-ins.

Thanks to you also. I tried holding the shift key down while double-clicking on FF icon but I still get the same message: "A restart is required to complete a previous installation of Firefox. Do you want to reboot now?" What is really strange is that I can't even uninstall FF and start over---running uninstall produces the same message as above.

Please see:

  http://kb.mozillazine.org/Software_Update (Software Update not working properly) 

Delete the files in:

C:\Users\<user>\AppData\Local\Mozilla\Firefox\Mozilla Firefox\updates (%LOCALAPPDATA%\Mozilla\Firefox\Mozilla Firefox)

(The above is for a windows installation - a Mac installation stores its files in /Applications/Firefox.app
To open one of these folders in OSX, Ctrl-click it and select Show Package Contents. )

Download a fresh copy of Firefox for installation.

Uninstall your current Firefox version before installing but don't remove your profile data when you uninstall Firefox (do not select to remove personal data) or you will lose your bookmarks and other data in the profile folder. Remove the program folder for Firefox as well.

Do a clean reinstall as an administrator. See:

http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

For information on your profile folder, see Managing profiles and:

  http://kb.mozillazine.org/Profile_folder_-_Firefox
  http://kb.mozillazine.org/Profile_backup

Please let us know how you fare.

edited to specify path difference on Windows

In trying to delete the specified files I got this far: C:\Users\<user>\AppData\Local\Mozilla\Firefox\ But the only sub-folder in "Firefox" is "Profiles"--there is no "Mozilla Firefox" sub-folder. I'll check the indicated references but am about to go on vacation for a week so it will have to wait. (Taking my laptop--Firefox is still working on that.) Thanks again!

Thanks for the suggestions--the one that worked was to use Revo Unintaller, which removed Firefox when other uninstallers failed (and also preserved my settings) and then I was able to install the latest Firefox w/o problems. Go Firefox, goodbye Chrome.