The change over to yahoo as the default search, as well as the ui changes a few years ago which made it a hassle to change search engines has, I would wager, done more harm to mozilla than whatever monetary benefit they gained from the switch. The fact that they made it difficult to change search engines is probably the worse offense. It's just blatantly anti user. i like firefox, but they needlessly erode people's goodwill toward them.
Firefox's primary advantage was that it was pro-user. At some point, it started consciously herding users by intentionally making certain choices that they didn't like which users made more difficult or impossible to find in the UI. That's a distinct philosophical break, and an open user antagonism. That didn't make it worse than other browsers; that made it the same as other browsers. The only criteria you're left to choose on are distinct features, and Firefox started methodically eliminating theirs. After the ending of the old extensions API, Firefox has finally reached its goal of having absolutely no advantages compared to any other browser, with the bonus of not working as well with google properties as the google-owned browser.
Then again I'll stick with FF for now since Google has managed to annoy me with their Chrome campaign and since FF is slightly better for my use cases and uses less resources AFAIK.
We are in quite a sad state regardless of which browser we use...
... the popups requesting your email address or that you turn off your ad blocker, the auto-playing videos (that relocate themselves as you try to scroll away from them!), the javascript hijacked page scrolling, and so on.
So really it doesn't matter which browser you use. Your browser is going to feel slow, and it's going to use a ton of resources.
