Are there any differences, feature-wise, between Firefox for Mac and Firefox for Windows?
There is a significant issue in viewing PDFs on web sites.

Adobe Reader for Mac has a browser plug-in for viewing PDF files. It's never been compatible with FireFox for Mac, or Safari 5.1 and higher for Mac.

With FireFox on Mac, there's no reliable way to view a PDF file that's on a link from a Web site within FireFox itself. The best you can do is download it and open it using a PDF viewer on your Mac.

With Safari, you can view a PDF file in the browser window with Mac OS X's built-in PDF display capability. It works well enough, but it isn't the Adobe Reader Browser Plug-in, and that can create some problems with services that depend on the Adobe plug-in.