Yep luckily the bug is being actively worked on and might land in the next version or two.
I can confirm its not fixed yet. Firefox Dev Edition is unusable on my 2014 MBP w/ integrated graphics but is crazy fast on my 2018 and Hackintosh.
Which is a shame - I really wanted to like Firefox on Mac.
On those same pages, Chrome and Safari work just fine.
If Apple were making MBPs better each year instead of demonstrating their "courage" ("This time we're taking X away from you because as long as Windows is the only competition, whaddya gonna do about it?") I would have already bought a new one, and that would presumably have more powerful graphics and not get as hot, but I would still want to verify that FF wasn't running the battery down faster than Chrome or Safari.
