I find that I cannot watch a YouTube video on my MacBook in Firefox for more than 10 seconds without the fans coming on at full throttle. This is one of the few reasons that I start up chrome, as strangely I can watch the same video in chrome without performance issues. I haven't had this issue on Firefox on PC
Google Sheets and Google Docs have been horrible on anything than Chrome for a while as well, and I guess they have no incentive to make that situation change. Firefox is dealing with it better than before I think, but I won’t hold my breath for parity to ever come.