Does it come with Mac performance improvements?
Reading the release notes:
Improved performance for Mac and Linux users, by enabling link time optimization (Clang LTO). (Clang LTO was enabled for Windows users in Firefox 63.)
Maybe in another few dozen releases they'll fix it. Doesn't Mozilla realize how many people develop on MacOS? Everyone I know develops on a Mac.
It seems like they are aware of the issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1404042
(I have the same issue and I'd like to switch to Firefox)
I use Firefox exclusively and have done so for the last 2 years or so. This sounds like it could be a driver issue for specific macs. Both my macs have AMD Radeon chipsets & quad core i7s.
Anyway, I'm sure this issue is real. Bugzilla ticket numbers probably exist for it and might be more helpful than vague complaints about things being slow.
Of course some web sites are a bit unreasonably javascript heavy these days. The downside of a large screen is that pushing a lot of pixels around is not free. Usually closing any offending tabs immediately restores any cpu usage I see. I'd suggest using the new task manager thingy (page menu->more->task manager)
When I switch to the "default" scaling (1440x900 and 1280x800, respectively), it stops. Only the 15" has a discrete GPU, eliminating that as potentially causal.
The "problem" scaling is 1.5x. The default is 2x.
If you have performance issues; you might want to check whether you need to blame the browser or some of your extensions.
This is a known issue, and has been around since at least v57. There are multiple Bugzilla issues on it. The cause is known. It isn't extensions. The fix is just invasive, and apparently ongoing.
The thread-parent absolutely cast a wider net than warranted, but everyone in this discussion who has experienced this problem knows exactly which one we're talking about, and the rest are all, "I've never seen a problem!" or "It's probably just extensions." Meanwhile, there's reliably a sub-thread somewhere in the discussion on nearly every article about Firefox, about this problem.
I find it profoundly ironic that you comment down-thread that "humans are very prone to confusing things which affect them personally with the general case" about a thing which you haven't personally experienced. You talk as if those of us for whom this is a 100% reproducible problem are an edge case, based AFAICT solely on your own not suffering it, coupled with your (not incorrect) beliefs about people poorly attributing performance problems in general.
That juxtaposition is really galling.
It's been like this for at least 2 years now on my MBP 2015.
That said, I've thought this before and turned out to be wrong. But it looks like it might be real this time.
I recently switched to Brave Developer Edition [1], which now supports Chrome extensions (which I need for work/pleasure). It runs circles around Firefox and Chrome, and maintains my privacy better.
Previously it was a tradeoff of getting speed (Chrome) or maintaining privacy (Firefox). For me, Brave does better on both counts, and now that it supports extensions I'm completely sold.
For pageloads Brave might do better if it blocks various stuff by default, of course.
This is one of the key differentiating factors of Brave. Maybe next time don’t lead with accusations of cognitive bias.