One aspect of Firefox that for now is superior to that of most browsers is the ability handle data that should be kept private. To enable the privacy features of Firefox on the Mac, click on the Firefox menu while Firefox is open and then click on Preferences. From here, click on the Privacy icon in the Firefox toolbar and then click on Always clear my private data when I close Firefox. This will clear cache, temp files, etc each time that Firefox is closed.
You can alternatively clear private data manually by clicking on Clear Private Data… from the Tools menu when you have Firefox open. This will clear data even before you close out your browser!