That sounds like the CPU is working harder than normal on that website. Test: Go to that site. Then go somewhere else. Does the fan slow down after a while?

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Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

At this time, the usage rate of the CPU and the rotation speed of the CPU fan do not become abnormally high. CPU utilization is 14-20% when problems occur. The problem is the rotational noise of the fan. Even if I intentionally lower the CPU or PCI fan speed, the volume of the fan noise does not change. When I lower the speed of the power supply fan, it becomes quiet.

https://www.google.com It also happens here. I also occur in Safe Mode, of course, delete profiles and configure new.

How old is the fan? Does the computer or browser have any problem?

Buy a can of compressed air and blow out the fan and the air vents.

Certainly my Mac Pro is 6-7 years old. But this issue is definitely Firefox limited. Other applications do not run away like this. Fans do not run away when I browse the same site with Brave or Safari.

I'm trying a rudimentary hardware reset, such as SMC or PRAM clear. These seem to have no effect. I created a new user account for macOS, and running Firefox on that account would still cause the fans to run away.

Is it a Retina display?

Enter about:config in the URL bar and set gfx.compositor.glcontext.opaque = true.

There is no Retina on Mac Pro. I tried the following.

• Disable hardware acceleration
• Disable "Stop access to the browser by the accessibility service"
• Limit memory on about:config

These were not effective either.

I can not affirm yet, but after updating to Firefox 67.0, it seems that the runaway of the power supply fan has stopped. I will observe a little more progress.

I'm disappointed. Immediately after the update I felt as if the runaway had been settled. That was just a coincidence.

This sounds like it could potentially be a hardware issue and not a FireFox issue. Granted your Mac Pro is 6-7 years old I suspect that has something to do with it.

Well, does it happen by chance only to Firefox?

Even with Final Cut Pro X or Parallels Desktop, which puts a strain on the Mac, this kind of abnormal rotation doesn't happen. They are not a power supply, and the rotational speed of the CPU and the fan of the PC slot increases. There is no abnormal rotation in Firefox of Parallels Desktop guest OS (Windows 10).

Why does Firefox only hit power fans? This is strange.

See also:

• https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

I downgraded to 65.0.2. It isn't a pure 65.0.2 because it is a profile that has been updated once to 67.

I was able to confirm that the runaway of the fan was settled in this condition. After that I used Firefox's refresh function to refresh my profile. There is almost no difference between 65.0.2 in this state and 65.0.2 immediately after downgrade.

And I updated it to 67.0 again. Then, the runaway of the fan started as before. If I return to 65.0.2 again, the rotation of the power supply fan will slow down.

I suggest you file a Bug Report here; https://bugzilla.mozilla.org/

See Bugzilla etiquette before commenting in bug reports. https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

Use the computer/profile having the problem. Give as much information as you can: what is wrong, what you tried, results . . . . List everything you can remember.

The website will read your user profile. No Personal Information Is Collected.

And post a link to the report here.

See the Firefox Task Manager (about:performance) page.

• https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox

Immediately after Firefox starts up or at the time of initial loading of the Web page, CPU usage rises by about 24-50%, but after a while, it becomes stable at about 1-3%. The Energy Impact itself also remains "low". I don't think that memory usage or CPU usage is a problem.

Thank you everyone. I solved this problem with 67.0.1.

That was very good work. Well done.

It started to occur again at 67.0.2. However, it takes less time for the fan to stabilize at a lower speed than before.

But it's really strange. The fan does not rotate as fast as Firefox when I use Final Cut Pro X or Paralles Desktop (Windows 10). When I launch Firefox on virtualized Windows 10, the fan does not rotate as fast as the Mac version. I check the energy impact on the activity monitor. So, for example, Parallels Desktop is 37%. Firefox for Mac is 9%. Firefox has lower energy impact than Parallels.

Maybe this is about the graphics processor (GDU) load and not about the CPU. Firefox 67 may be using WebRenderer and passes more tasks to the GPU and thus you ca get a lower CPU usage.

See also the graphics section on the "Help -> Troubleshooting Information" (about:support) page.