@wgotto, Nothing too profound. I have tried various suggested solutions - decoupling one CPU, rebuilding a profile, removing add-ons, etc, on several machines - personal, work and test lab. Firefoxes of various vintages seem to work, then get to this (not responding) point and the only option is to restart it. People can only share what worked for them (if they come across this thread) but we don't know if they subsequently had this problem. I use FF only because of some developer/accessibility/seo add-ons but now defect to IE9 and Chrome for non-work browsing.

Ok. My daughter who has a Mac had problems with Firefox & she went to Google Chrome. She's pushing me hard to do likewise.

DID YOU HEAR THAT FIREFOX ? Do you want to remain a popular browser or a footnote in internet history ? A has been ? A wannabe ? Sheesh.

I really don't think Firefox knows what the problem is or how to fix it or they would have by now. The fact that so many different things seem to cause the problem makes me think there is a common thread among them but Firefox doesn't seem to know what it is. My problem was Carbonite Online Backup. Once I changed the settings to prevent it from backing up all the time to a scheduled backup when I wasn't on the computer my problem went away.

I hear ya there. But as you say - so many things seem to be causing it - because I had the problem before I had Carbonite. I'm just going to have to try another browser I guess.

See what I mean? I am not sure I have heard of Carbonite, unless it is a backup service over the web. I wouldn't use any such service on account of the slow 1.5 M/256k connection I have. I have seen the problem without using Carbonite at all.

If these were the Windows 98 days, I'd be thinking that FF causes a memory leak, but with Windows XP onwards, memory leaks have decreased to the point that you hardly hear that term. But the system behaviour is very reminescent of those days -- the longer you use FF, e.g. an all-day browsing session on a weekend (or at work) is guaranteed to cause this error.

Yes that is exactly what it is. Too bad you can't use it. I have had several different methods of back up over the years but the weakest link in all as ME ! LOL !! I'd forget or put it off & then BAM ! A HD dies & data goes to software Heaven. With Carbonite & the other one - Mosey I think - you create or change a file & it's backed up instantly or nearly so. Plus if your house burns down - even the most diligent back up person is screwed. Not with these online companies.

Man I haven't heard that term (memory leak) in ages ! LOL !! I'm pretty happy with Bill's latest OS. I never even had problems with Vista but I know that is rare.

I think I will begin to check out IE 9 & if that doesn't get me excited I will check out Google Chrome.

Far too many theoretical "solutions" that might have worked for an individual, but none seem to point to a common root cause... So for, most of these "solutions" do not apply to my situation...

Try the applet "WhatIsHang.EXE" to get a dump of what is happening during the "Not Responding" sessions -- for me, I keep seeing a "recursive loop" error, that evidently implies that some part of Firefox internal code does not have an efficient time-out exit point.

Thank-you NYC-HDL but that's above my level of expertise. If Firefox can't fix their software - I'm outta here !

Google 'firemin'. It fixes the memory leak in firefox. It worked for me, firefox no longer hangs and I don't see 'not responding' anymore! Yipee!

I can't see it in the Firefox blog but I recall in the past two days there was an announcement about a future release that will solve this problem by making it easy to set up a new profile and preserve your settings.