I think no matter the faults of Firefox, that for its function while ignoring faults, it's more usable than other browsers, and considering those faults, it gives freedoms to override those faults. These freedoms have to do with Mozilla licenses, which comes from them, and gives the freedom for forks that don't have those faults. A problem with that is that, it takes a lot of initiative for a new product to be made from it.
The Mozilla licenses from the organization of the same name are better than GPL, yet are a little complicated, because of the way MPL2.0 is made compatible with GPL. There may be little or no other way to do that. The core principle of Mozilla licenses are great though. It gives freedoms for software on how it can be used, and what it can be used with. It's somewhere between a BSD license and GPL, and the best part is that it's non-viral, except where the parts make it usable with GPL. MPL1.1 is funny though, because it allows an upgrade to MPL2.0, if the authors choose, and that brings it into the odd GPL sphere.
Because of the freedom of the license made by the developing organization, I don't think it in itself can be evil or horrible at its core, but it can have deep rooted faults. I think the license speaks to the principles for Firefox. Evil contributions can be made, but the core purpose by Mozilla wouldn't seemingly be against the principles of the license of that browser and the steward organization.
Firefox may not be Unix, it's something between Unix, Sun/Oracle (CDDL) and GNU (GPL). I'm not sure what "it is something horrible" implies. I'd like to see an ecosystem between BSD, CDDL, LGPL and GPL that's simplified, even if it makes it incompatible with GPL (and in my mind, that incompatibility won't be by much and it will be the fault of GPL's viralness than the more ideal license, as it would almost be compatible), and even if it's not Unix, but it would be very Unix-like or Posix-like.
Functionally, to protect code in necessary ways and allow freedoms of use, Mozilla licenses work for that. I think there's a better way, even if that way is barely incompatible with the GPL due to if its viralness forces other licenses to be submitted to GPL for them to be compatible with GPL. If that's the only way to make them compatible, it's better to work with existing compatible licenses, such using a better license in conjunction with CDDL code. LGPL is functional in this way too, except until its license says it can be re-licensed into GPL in a one way street (ironically, many permissive licenses fall under that). The Faq says, this re-licensing makes LGPL compatible with GPL, which is the only reason I would make a license compatible with GPL, except for the relicensing part. If you want to relicense to GPL, you already have LGPL and you also have some complex compatibility with Mozilla2.0.