I love Seamonkey (I have to reinstall it on this machine as I haven't used it in a while), but it's also behind the Firefox dev cycle and doesn't offer the same level of extension coverage that Firefox does.
It'd certainly be very interesting if the could maintain the latest browser fixes (even with less extension compatibility), but I doubt the team has the bandwidth to keep that up.
Just installed it. It doesn't support High DPI displays on Mac OS X. Unfortunately, that's a bit of a blocker for modern Mac laptops (everything looks fuzzy).
