My Mac Book Air 2010 seems to run quite a bit hotter with Firefox 4 when hardware acceleration is enabled. While playing with FF4 (released version) tonight, I noticed my fan running quite a bit more than usual when browsing web sites, so I looked the CPU temperatures and confirmed both cores were running hotter than normal. Within specs, but bugged me...also probably drains the batteries faster. So I've disabled hardware acceleration in Firefox's preferences for now. Would be curious to learn if anyone else notices this....and if users are also seeing a battery life penalty when using FF4 with hardware acceleration turned on.