Re-name the prefs.js file to something else like prefs.js.old1 because that will reset all your preferences to default settings. (If you have a lot of customised settings we can work with the old file to try to reverse just the very recent change that caused the fault, especially if, when you view that file you remember what it was you changed)

Reset Firefox preferences to troubleshoot and fix problems

Renamed the prefs.js file to prefs.js.old1; did not see a user.js file nor a prefs.js.moztmp. There is a sessionstore.js, but did not alter that file. Firefox still crashes on startup. It did create a new prefs.js file (new one only 4K compared to previous 11K file). When presented with the crash report window, chose to restart Firefox; crashed again. Next time, chose to quit. Then started again in safe mode. Two new crash reports: bp-a4da3e73-292b-4629-8f39-ad2ea2141013 & bp-914ca3f4-6f32-46eb-a646-587492141013

Well, it was worth a try! Any other ideas? Thanks ...

Thinking about the profile issue prompted me to troubleshoot by creating a new profile for this user. Closed Firefox and started the profile manager from a command prompt [firefox.exe -p]. Created a new test profile, unchecked the "Don't ask at startup" option and started Firefox. I do get the "Firefox - Choose User Profile" dialog box, but even when I select the new test profile Firefox still crashes at startup. New crash report: bp-5523b9e5-c121-4814-b9aa-f28792141013

See if this helps;

http://support.microsoft.com/kb/980922 Some stability issues occur when you run an application that uses the DirectWrite API

You can try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

You need to close and restart Firefox after toggling this setting.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

Had to call off the troubleshooting for a while to give the user a chance to get some work done. Hope to have some time again later this evening for more troubleshooting. Will give this a try then. Thanks for the suggestion.

The DirectWrite issue doesn't appear to be the problem. The page for KB980922 shows hot-fix versions: Dwrite.dll 6.1.7600.16539 1,533,440 27-Feb-2010 15:03 x64 Dwrite.dll 6.1.7600.20655 1,537,024 27-Feb-2010 15:12 x64

This system is showing a more current version: DWrite.dll 6.2.9200.16571 1219 KB 28-Mar-2013.

Thanks for the suggestion, though.

The hardware acceleration setting appears to be the culprit. After unchecking the Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available" setting, Firefox no longer crashes on startup. Initially I'd glossed over this setting since it isn't an issue for any of the other users on this system. I'm still puzzled as to why this would be an issue only for this user, and what had changed as of this morning that set it off, but obviously there's something about their configuration which triggers this situation, even for the default plain vanilla Firefox profile! Thanks, cor-el!

it isn't an issue for any of the other users

There are many users that use Hardware Acceleration with no problem. Unfortunately, there are many that must turn it off.