Lots of us do. Firefox is my browser on all my devices. I do use Chrome when visiting Google Docs which I assume is deliberately sabotaged on Firefox though.
Might just be that Google doesn't test on Firefox and also maybe are "to smart for their own good" coming up with out of the box solutions that can be more likely to fail to begin with. Maybe I'm being overly optimistic, but I kinda read myself as saying "they probably just don't give a sh!+."
It's not deliberate; it's lack of investment. Docs is complicated enough that the small deviations in browser implementation add up---to make something as complex as Docs not work in Firefox, all you have to do is be willing to publish without hating new features on FF end-to-end tests.
I have a different experience with that: on a current MBP, Google office suite software (docs, slides, agenda, mail etc) regularly uses 100% cpu in safari for no apparent reason, and clearly also has some memory leaks were single tabs bloat to 2-3 gig memory... Have to kill the the threads manually. I would say it’s fairly unoptimized / pushes you to chrome
I second the experience of the other commenters. Keep it open long enough and it sucks up all the resources in non-chrome browsers. I also include Google Slides in my experience btw. It is more severe with Slides than docs.