I like SeaMonkey a lot, but I'm quite worried about its long-term health. They've had a lot of trouble building new releases lately.

It also takes a lot of work (not just userchrome.css hacks, but outright extracting omni.ja(r) [and its intentionally corrupt header that prevents most tools from being able to extract it], hacking at the XUL layout, etc) to make it look even remotely like it belongs in 2015 (the default is right out of 1995.)

And then there's quite a few serious limitations. The cookie manager is all but impossible to use, there is no web inspector (required to use Adblock well these days), no network debugger tools (great for writing/debugging web servers), fullscreen controls don't work at all, etc.

That said, SeaMonkey's probably my best shot going forward. I keep trying to switch to Chrome, but it's just so darned inflexible.