Firefox clogs my CPU with all cores on my Mac Snow Leopard 10.6.4
I usually browse the web heavily as I open around 300 tabs sometimes. However, with the recent update of Firefox, I have 3.6.8 running on my latest Mac Snow Leopard 10.6.4; soon after I open my browser it becomes deadly slow after a while. The activity monitor shows Firefox eating up all cycles on all cores. I noticed that this happens after I open a site with flash or an applet in it, but not sure though. It also crashes.
Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems
If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Diagnose Firefox issues using Troubleshoot Mode start window to disable all extensions. You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")