Here's my perspective on this - Chrome has established itself as the baseline. The baseline is no longer the W3C standard, it's Chrome due to all of the experimental future W3C spec items being in Chrome. Chrome leads the spec, and with its 70% market share developers allow it to. Firefox will always be playing catchup because of this, regardless of their market share. This leaves three main reasons for using Firefox…
We need a better way to communicate this: Chrome doesn't "lead the spec", it "rushes out ahead of the spec". The developers using non-standard features need to be held better accountable for using non-standard features, and Google needs to be held better accountable for releasing non-standard features ahead of standardization processes. W3C is seen as no longer relevant to HTML specs having delegated "HTML5" to WHATW…
If devs want to make something, Chrome wants to make it happen, and I want to use it, then I don't want Mozilla trying to block up the whole works.
Especially not to "protect my privacy" from a site I completely trust, that might even be an intranet site I built myself.
What's next, are you going to disable downloading executable files, probably the most dangerous browser feature of all?
There's no nice alternative, or sometimes no alternative at all besides making a native app for a bazillion different platforms.
Maybe WHATWG actually isn't just rubber stamping things because they're a google puppet, but at least partly because... it's what devs want.