When I interned at Mozilla, most of the FF devs developed on a Mac. They are not ignoring the platform. I suspect the issue is as other said, low incidence, high impact.

It seems like they are aware of the issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1404042

To be clear, this doesn't affect all macOS users. My battery reliably lasts a whole day with Firefox running throughout. That said, the subset of users who are affected, like you, suffer a lot - low prevalence, high impact.

In my case, CPU usage goes to the roof if I use a scaled resolution instead of the default one. If that is the case with all macOS users with non-default resolution, I wouldn't call it low prevalence.

You can work around this (not ideal I know) by enabling "Low Resolution" mode for Firefox only: https://support.apple.com/en-us/HT202471

(I have the same issue and I'd like to switch to Firefox)

Not an issue for me. I have a imac 5K and a retina mac book pro. Both with image scaling on by default. I think most recent macs have retina now.

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)

Anecdotal, but I've found it happens when image scaling by a factor other than 2. Affects my setup of a 4K display at 2650x1440 effective resolution, or 1.5x scaling.

Exactly this. I run at 1920x1080 effective resolution on my 15" rMBP, and 1680x945 on my 13". I see the issue on both.

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.

I use only Macs by default. It runs great and has for years. There's probably a real issue somewhere but it's far from as universal as your post implies.

Likewise. Not aware of any weird issues with performance in relation to Firefox. I use it exclusively. I'm on the beta channel. I can't remember the last time I had a browser crash. I generally restart it to apply new updates every few days or so.

If you have performance issues; you might want to check whether you need to blame the browser or some of your extensions.

Seconding your last point — almost every time I've had someone complain about generic Firefox or Chrome performance the problem went away as soon as they restarted it without extensions. There are certainly exceptions but misattribution is common enough that I'm not surprised to see browser vendors adding the UI to make it easier to discover.

This specific problem is one of those exceptions.

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.

That’s true but not what this thread was about. The person I responded to above was making a very broad claim, which is wrong, and jillesvangurp agreed with the observation and added a general point which is correct. There is a specific issue affecting a subset of people with less common configurations but that doesn’t make the sweeping claim true or the recognition that browser performance issues are notoriously poorly attributed untrue.

No, it's specifically what this thread is about.

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.

I was aware of the issue already but that’s also why I knew that the biggest impact comes from a non-default setting. I never said that it wasn’t a real problem, or that it doesn’t warrant attention — only that it wasn’t as broad as claimed and that is a very common problem with browser issues because everyone uses them but people who don’t have problems generally don’t go around posting that everything is fine whereas the percentage of users who are affected will complain regularly.

Scaled resolution option is so widely used that it might as well be broken entirely.

Do you have data supporting that claim?

Do you require a scientific study for any fact? If you bothered to do any googling, or whatever Mozilla equivalent of google is - this is in the top 3 results. https://9to5mac.com/2016/12/02/15-inch-macbook-pro-screen-re... Scaled resolution is defaulted on a huge amount of Macs.

I asked for data because humans are very prone to confusing things which affect them personally with the general case. Since Mozilla uses telemetry heavily I tend to trust their prioritization more than random self-selected commenters.