Firefox's lack of HiDPI support was killing my eyes, but I've been using Nightly builds and they look great. The only problem I see is that Flash plugins get confused about screen sizes (so YouTube has tiny control buttons).

The plugin support hasn't bothered me yet, and it's almost surprising.

The amount of flash I use on a daily basis is so incredibly minimal these days. I've started using the built in plugin blocking with firefox. The only time I really turn it on is for Netflix and the occasional video that isn't part of the HTML5 beta on youtube is about it.

( not that any of this is an excuse to not fix the bug :P )

As Google Chromes GWT Developer plugin is noticeably slower (and stopped working altogether) than that of Firefox's, having to use non-retina supported browser for GWT development is annoying.

I usually start up a Chrome private browsing tab for Flash stuff, and use Firefox for most other stuff.

netflix is silverlight, not flash, though this is tangential to your point