> its performance leaves a lot to be desired

I'm not sure what you're talking about; this may be the case several times in the past, but you should check again because this is a thing that constantly changes. Firefox performance today doesn't really leave a lot to be desired IMO

> Microsoft Edge got a decent native vertical tab solution before Firefox did! Edge!

Tree Style Tabs has been around since like… 2007?. Or does the "native" part somehow make it a whole lot better?