Google's rejection of web standards and attempts to put in their own standards is half of what breaks shit anyway.
I'm glad they're working with the G Workspace team, but Holy Hell, it's been clear for a long time that Google, the company, isn't a friend to Firefox, even if individual developers are.
They mainly pay for top search spot in Firefox as a bulwark against claims of monopolization.
Really? I've used Sheets in Firefox weekly for years and never noticed any major issues. I do a lot of copy paste, but not a lot of cut and paste, but I'm sure I would've noticed that.
Could it be one of your extensions? Aside from some general slowness, I haven't really had any issues with G Apps in Firefox.