> what exactly are the complaints with Firefox?

If you are a (the) leading browser like Firefox once was, the "what are the complaints?" is the right question.

If you are a minor browser like Firefox currently is (~2.5% market share), the "what is it doing better?" is the correct question.

My primary complaint is that they have a bunch of ad placements on the product out of the box when it's opened for the first time and any time I set up a new system I have to go configure Firefox to not be annoying by default. It makes the Firefox experience feel subversive and untrustworthy because this freshly installed application is obviously bedfellows with advertisers. I know I can't trust advertisers with my data or browser behavior, so why should I trust Firefox with it? If I stop using Firefox for a little while, they _so helpfully_ offer to reset my configuration back to default so those ads will get shown again. It's a hostile experience.

Additionally, my perception (from posts and discussions like these, I'm not a financial analyst and I have no meaningful insights into their business) is also that they probably receive enough funding through non-advertising means that they don't actually need to do this if they were to pare back the nonsense spending they're so greatly known for.

Hum.

I have at home 13 year old hardware running Firefox and no performance complaints.

Major problems with Firefox include:

  - full uBlock support

  - the ability to still be themed

  - first-party isolation

The common wisdom is that overall Firefox can feel bottlenecked at render and draw times (“less snappy”). That could be a result of a slower JavaScript engine (takes longer to get to drawing), or a result of poorer hardware acceleration (slower drawing), or a less optimized multiprocessing/multithreading model (more resource contention when drawing).

I honestly can't see it in the real world, but synthetic benchmark are pretty clear on that front.