There are a bunch. I’ll see if I can find the exhaustive list, but you can look for it by searching “Firefox disable telemetry flags about:config” on your search engine of choice.
FireFox does collect some data, even in incorgnito, and even if you opt out of optional data collection. Last time I checked, you had to change a hidden flag (about:config) to truly stop them from collecting all data (and they could technically re-enable it in future updates).
There are a bunch. I’ll see if I can find the exhaustive list, but you can look for it by searching “Firefox disable telemetry flags about:config” on your search engine of choice.