I use Firefox on MacOS. It is easily as fast as Chrome for me (and I have tons of tabs open in multiple windows). And I use Google Docs/Sheets/etc. all day long with zero slowdowns.
I use Firefox on MacOS. It is much slower than Chrome for me (and I don't tend to hold open many tabs or windows). I use Google Mail/Groups/Calendar all day long which became unusable in the last months.
Open your email in thunderbird or move your email somewhere else. This is all part of googles game. They slow down youtube in every other browser as well.