I prefer to use Safari as my web browser on the Mac because it is so much faster than FireFox. Unfortunately, Gmail does not work reliably in Safari. For example, the address book auto-complete does not always work, or worse, hitting the send button sometimes hangs (this got me into trouble a couple of times where my email to say cancel a meeting never reached the other party). I think the problem is with the way Safari handles simultaneous XHR requests. The ‘send mail’ request gets queued up behind other in-flight XHR requests. Perhaps Gmail should have different priorities for XHR requests and high priority ones should jump to the front of the queue or even preempt in progress requests.
Note to mozilla developers: speed should be #1 priority, just ask Google.
Also: does it make sense to call Safari and FireFox web browsers? In this context, they are more like web application containers or runtimes.