After a few annoying Firefox crashes I figured out that Shockwave Flash was freaking out on me. 

How I Figured It Out

I figured out it was Shockwave Flash plugin by visiting seveal gaming sites and watching the cursor spin and spin.  I had to Force quit the browser on my 10.6 by going to Mac->Force Quit->Firefox.  I restarted Firefox and disabled all the add-ons by Firefox->Tools-Add-Ons.  Went back to a gaming site.  The site asked me to install Flash.  I then re-enabled Shockwave Flash 10.1.x and watch the browser crash.

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