hello, to further diagnose the issue, can you please test if the hangs are also occuring when you are running firefox in safemode? Diagnose Firefox issues using Troubleshoot Mode

yes it hangs even in safe mode.

ok, this may be the strangest bug i ever heard of. i would try to download the latest drivers for your soundcard & graphics hardware, uninstall abobe flash with the uninstaller they provide and reinstall it from http://get.adobe.com/flashplayer/. another thing would be to try disabling all plugins in firefox > addons > plugins for testing purposes and see if this does make any difference.

in case this does not solve the issue it would also be interesting to know what is going on in the windows task manager (ctrl+shift+esc) while firefox is hanging - is firefox.exe or any other process is spiking to 100% cpu usage or is there an exceptional amount of memory occupied?

Which security software (firewall, anti-virus) do you have?

Does it also happen if you boot Windows in Safe mode with network support by pressing F8 on the boot screen?