I recently started using Firefox Aurora after years with Chrome, so I'm not a loyal FF user :) What made me switch is vimperator, I really like being able to navigate with the keyboard when my MBP is docked and issuing commands by their name(e.g., I can add a page to pinboard with `:pin`), also it saves some screen space by removing the navigation toolbar. Another nice feature is macro-recording, if you are doing a very repetitive task you can record a macro and run it when needed.

Obviously FF is far from the perfect browser, I hate that it doesn't use native ui elements on web pages(e.g., the `select` html element) and I think it's a bit more resource-hungry than Chrome.