I've been having the problem with as few as two tabs opening. The only time it does not do it is in safe mode. I have cleared my history, turned on the plugins one at a time, and run virus check. With any plugins turned on, it hangs every couple of web pages opened.

My results are also the same with and without plugins. I've wiped the installation clean and reinstalled. I've done a lot of option and config tuning with no improvement.

It is better if the pages have been previously loaded; then I can open more pages simultaneously.

One other thing I've noticed is that Firefox seem to run at lower priority than before. If I have a resource-intensive app running (a compiler, for example), Firefox seems to just hang (can't get a popup menu to open) until the app yields CPU. I ran Firefox 4 and 5 while running the same compiler and never saw this behavior.

I get this problem and worse... It seems to be time dependent rather than tab dependent, all of a sudden Firefox stops accessing the internet and refreshing content. Other applications continue to do so OK and there is nothing obvious in Windows firewall. Closing Windows firewall makes not difference.

Closing Firefox does not help it keeps running in the back ground and even Process explorer or task manager cannot shut it down, the computer won't shut down and has to be powered off by holding in the power switch. None of this ever happened before the last upgrade. Upgrading to 6.02 has not fixed it either.

Seems to be even worse in 7.0 and safe mode makes no difference for me.

For a temporary solution I've been using Firefox 5.0 , but I would really like to see a real fix for 7.0 =/

As a Systemadministrator I have to manage many client computers and I experience this problem on windows xp and windows 7 since firefox version 6, but also had this problem in version 4 and 5 sometimes. Even if I fresh install a new 32bit windows xp virtual machine, install firefox 6 (e.g.) and take the challenge opening 5 tabs simultaneously my firefox takes all of the cpu core it is running on and I can't open any new site. Even if I then kill my firefox, start it again and try to restore my last session (very important for me, because I work with 50 - 200 tabs per windows normally!) I can't reload my opened sites.

I even tried the safe mode without any addons or plugins..no luck..

So many people experiencing the problem, but no one of the developer community can't retrace this?

I have the same issue since upgrading to version 7. For me, installing 6.0.2 over 7 brings back the functionality.

Finally found a fix that is working for me! I've been using it for the last 10 mins or so and has not crashed/hung once yet!

Go to about:config and change the max connections from 256 to 48. The setting is "network.http.max-connections" Found here: LINK

So far so good. Please comment if this works for you as well!