Just a heads up, but we are actively working on improving the situation here, and should have releases coming out that steadily and progressively improves the experience on this front. It is an area of major focus after the initial Quantum Flow effort, and we have technical fixes in many places in the pipeline to address this.
(I work on the Javascript engine in Firefox, and improving our story here is one of my personal top priorities, as well as an organizational priority).
Are you saying that performance issues on Google properties are a bug in Firefox? The other posters were implying the issue was Google doing things to intentionally slow down performance in Firefox.
I'm not about to speak to the intent of programmers I haven't interacted with heavily. In these sorts of charged conversations there is often an impulse to make issues about "this" or "that" exclusively. I find it useful to avoid that impulse entirely and instead focus on what I can do to make things better.
Not stating Google is intentionally slowing down things - but I've noticed that Google products and only Google products are slow to render, slow to click into the search field of Google Maps, and when I press 'compose' within Gmail on a macbook pro 2017 I can wait easilly 10 seconds before the email bit pops up. Within Chrome however, quick and slick.
Google has a history of disabling or degrading features (image search, maps, youtube) in browsers that aren't Chrome under the "we haven't fully tested them" excuse. In almost all cases changing your user agent to Chrome would result in a perfectly functional site. Perhaps there is 1 feature that didn't work but it was usually obscure and it feels like Google was just throwing the baby out with the bathwater to spite anyone not using Chrome. Up until recently it felt like Google made a Chrome version of their product and a lowest common denominator version and anyone that isn't using Chrome got the later. Now it seems like they let some browsers use the Chrome version but there are unusual performance regressions compared to Chrome. It's very reminiscent of the first browser wars where sites were IE or Netscape only.
The whole point of standards push over the years was so that developers could just code to the standard and the browsers would either catch up or suffer the consequences. It seems like these days Google is dipping into Microsoft's old playbook for every trick it can find to get people to switch to Chrome.
If you want a site the is just horrible in Firefox Mobile, try: http://www.bom.gov.au/australia/meteye/ This is a Australian Government site, so there is no Google shenanigans going on here.
You are meant to zoom in on a locality on the interactive map, and then pan around by dragging. Panning works fine in Chrome. The panning is so slow in Firefox Mobile it's unusable . (It's fine on Firefox desktop, but I'm guessing the shear horsepower available on a desktop CPU hides the problem).
It's a bit sad, because it's a page I use a lot. Whatever it is, it effects a lot of similar pages.
(I work on the Javascript engine in Firefox, and improving our story here is one of my personal top priorities, as well as an organizational priority).