If you are having problems with Firefox 3 hanging or crashing, one of the most likely culprits is an incompatible extension or plug-in. The easiest way to check for this is to disable all of your plug-ins and extensions and use Firefox 3 to see if you still have problems. You can do this by going to Tools > Add-ons and selecting the Extensions and Plugins panels, highlighting an extension or plug-in, and then pressing the Disable button.

If so, then it's likely a problem with your caches or download history. The easiest way to fix this is to clear all of your private data by going to Tools > Clear Private Data... and clearing out everything.

If disabling the plug-ins and extensions fixes the crashing problems, you then need to start enabling extensions and plug-in one-by-one until you find out which extension or plug-in is causing Firefox 3 to crash.