Thanks JacobBruce for your solution.

At present the problem seems to have disappeared as mysteriously as it (re)appeared. So I will wait and see. But if it comes back I will try CheckMate's solution. Thanks.

I was having the same problem.... But I keep forgetting that when you upgrade firefox... or it updates automatically... you need to right click on the firefox start up icon, go into properties, click on the compatibilities tab, and put a check in the "Run This Program As An Administrator" box, then hit apply. Start Firefox, and it should work OK. Problem is...each time you upgrade firefox and/or I think Adobe flash... you need to make sure that box is checked. This is on Firefox 15.0.1 with Adobe Flash 11.4.402.278 all up to date, Windows 7 64bit. If Firefox has Adobe flash add-on, it needs to run in admin mode or it will crash.

cutmetal,

Checking your username for previous posts (here) I see that you also posted the same information in a number of other threads today.

You don't normally need to check the "Run This Program As An Administrator" box in Firefox -> Properties -> Compatibility tab, to prevent crashes after updating Firefox or Flash. If you need help with this issue, you should ask a new question. You can use this link as a starting point: https://support.mozilla.org/questions/new

Well, I checked the "run this program as an administrator" box and the problem stopped, After about a week I thought I'd see what happened if I unchecked the box, and the problem started again. So I'll keep the box checked, even if it makes starting the program slightly slower.