The game clients are all identical, and all work the same except for a small segment of code that talks to the drivers (those have to be native to the OS). With the release of Lion, it became pretty clear that java on the the older OSX versions doesn't behave like they should.
For non-steam users, you can try using -Xmx 512M to force a larger heap size using the system java settings (don't know the process off hand). But it does have a side effect if you use java heavy websites, since each java instance will start chewing up memory if left running too long.
same here
2.53 GHz Intel Core 2 Duo
4 GB ram
NVIDIA GeForce 9400M 512 MB
Mac OS X 10.6.8
for the most part fire makes me lag makes FCS a pain
btw i run from steam if that helps