Hmm. That's very bad.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Okay so I have Noscript and I noticed when I allow scripts for pages that also causes the system to lock up. Could javascript or something be the bastard causing this to happen? How can I stop it from screwing everything up?

Java Downloads for All Operating Systems

Make sure your Java (Not JavaScript) is up to date Verify Java and Find Out-of-Date Versions {web link}

It says it's up to date.

How often does it happen? Having the exact problem you described, but it only happens once per boot

Wizzlbang said

How often does it happen? Having the exact problem you described, but it only happens once per boot

Yeah, it the same thing for me. It's weird and it's kinda frustrating that I can't figure out how to stop it.

Have you done the above? What were the results?

What web sites? Please post public links for us to check out.

Do these pages have videos on them? Flash block {web link} Never be annoyed by a Flash animation again! Blocks Flash so it won't get in your way, but if you want to see it, just click on it

I have this exact problem aswell. I use Adblock plus, and I have Flash disabled by default. so I know that neither ads nor flash programs are at fault for the issues we are having.

I know this isn't an issue for all systems, but it's worth a try for sites where you allow Flash: Disable the "protected mode" feature. This feature of the Flash player plugin has security benefits, but seems to have compatibility issues on some systems. There is a hidden setting for switching it on and off:

(A) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(B) In the search box above the list, type or paste flash and pause while the list is filtered

(C) Double-click the dom.ipc.plugins.flash.disable-protected-mode preference to switch its value from false to true.

This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox.

For one-time-per-session lockups, in earlier versions of Firefox some users discovered this was caused by having an enormous font collection. For some reason, when Firefox visits a site that uses a downloadable font, Firefox enumerates all of of the fonts on your system which takes a long time. However, it only does that the first time during your session (i.e., the problem does not repeat until you close all Firefox windows). Not sure if this issue has been fixed in recent versions of Firefox or is still a problem.

For me I noticed it started happening right after I downloaded a long list of windows updates, not sure if thats just a coincidence or the reason.

It usually seems to happen on high content websites, twitter, tumblr, deviantart, etc. Whether or not they have a flash plugin doesn't seem to factor into it.

There are one or two Microsoft updates that have caused problems. I don't remember what ones.