When styling a form element in Bootstrap 3, it renders an ugly button on the in Firefox on OS X:
There is a slick-looking jQuery plugin that apparently plays nice with Bootstrap called SelectBoxIt (http://gregfranko.com/jquery.selectBoxIt.js/). The thing I like about it is that it allows you to trigger the native select box on whatever OS you are on while still maintaining a consistent styling (http://gregfranko.com/jquery.selectBoxIt.js/#TriggertheNativeSelectBox). Oh how I wish Bootstrap provided this option!
The only downside to this is that it adds another layer of complexity into a solution, and additional work to ensure compatibility with all other plug-ins as they get upgraded/patched over time. I'm also not sure about Bootstrap 3 compatibility. But, this may be a good solution to ensure a consistent look across browsers and OS's.