In firefox, click Help >> Restart with Ad-ons Disabled....
This will disabled all installed addon-ons temporarily. Check if you still experience problems. If this fixes for you, Restart firefox in normal mode, and disable addons one by one to check which addon is causing problem.
Alternatively, as you said disabling java fixed it in IE. If java runtime installed in your system is older version, this creates problems while browsing sometimes. Download latest version of java from
http://www.java.com/en/download/manual.jsp Download the Offline installer for windows. be sure all your browsers are closed when you run the installer.
You can first remove java from 'add/remove programs' (windows xp) / 'Programs and features' (Windows vista and above). Installing latest version manually sometimes keeps the older version also installed in your system which is really of no use.