Don't forget that those to the right of the spectrum also care about politics, just the viewpoint is different. Both sides are necessary (along with debate and discussion) to achieve a rational path in most cases.
FF has taken a few extreme stances to the hard left on a few things, which irritated quite a few (in some cases, this was enough to push a chunk of people over the "effort to switch to a new product" threshold). However, I think you're entirely correct in your assessment that it's mainly them messing around with the API, the look and all kinds of things.
Browsers are now commodity, and pretty standards based. If you're doing to push far outside an general standard, there needs to be a good reason (as a default); the pitch these days is to established companies and an open standards based environment now, not as it was 20 odd years ago when change was the driving factor and new was the biggest draw.
What many others in the threads object to is the reliance on the Chromium engine, which is a Google set up entity that is similar to the Chrome browser (and this is the engine behind Microsoft's Edge, and the majority of other browsers; FF was one of the few that doesn't use that engine).