I'll stay out of the browser discussions, but will only add that any serious software developer will have IE, Firefox, Chrome, and Opera installed on their system.
Apple is the driving force behind CSS3 because many of the CSS3 enhancements are built into its OS, and the Webkit rendering engine is built around those functions. Those CSS3 enhancements will ALWAYS be faster on Chrome/Safari than on any other browser, and they will be the fastest when using a Mac.
The developers of Firefox, IE, and Opera are the controlling force of W3C. That may change in the future, but for now, any CSS3 proposals not in FF3.6 have NO HOPE of being adopted. A few others will probably be dropped from future versions of Firefox and will not make it into the CSS3 specs as well. The ones in question are those built into the core of Mac OS. There's precedent here. Microsoft tried to ramrod the IE filter properties into the CSS2 specs and were shot down -- it would have given them a competitive advantage since those functions were built into the Windows core. Apple was the biggest complainer at the time...funny how things change in a few years.
There's an old saying...the reason to learn from the past is so you don't repeat it. I guess Apple never heard the saying.
This is why I stay away from using any CSS3 property that is built into the Mac OS core, because it will NOT be part of any CSS3 spec. Why write software that will only work on 1/3 of the browsers accessing the internet?
Most of my browsing is with Firefox. Ego-one has always been slow for me. The sidebar didn't seem to change things, but then again, a speed drop from 4kph to 2kph is a 50% drop but wouldn't be noticeable...