Re: SeaMonkey: it just works....
Another long term "SeaMonkey" user here. It does everything I want it to, it's as customisable as Firefox used to be, and the project leaders are adamant they won't adopt any Firefox "features" or UX, unless they absolutely have to.
It's essentially a community led continuation of the former Mozilla Suite (which in turn was codenamed "Seamonkey" in the early days when Mozilla.org was still just an offshoot of Netscape) that was effectively abandoned by Mozilla.org several years ago in favour of promoting Firefox as their official product.