And I'm not using it to "stick it to Google" either. Containers and tree-style tabs are a huge productivity win.
Also, TST isn't a FF-only feature now (Brave has started the rollout, Orion has a great implementation, and Edge has it also).
My personal path was decades with FF and its predecessors, then Brave because it was much, much faster. Now I'm debating between Orion (which might win on performance/battery, due to being webkit), Brave (which is fast, and is evolving its TST capability), and Firefox (which works fine, but IME is a bit slower).
Over the same time period, web browsers have gone from a hot new technology to a part of daily life for most people in developed countries, and that's created areas for conflict where someone at Mozilla is trying to figure out how to retain users against a hostile trillion-dollar company and coming to conclusions which are different than some of the more conservative members of the user community want. We saw this with things like XUL's deprecation where that feature was blocking a lot of improvements which benefit 100% of users and a small group of users felt very strongly that someone else should do the extensive amount of work needed to maintain and modernize a lightly-used feature.