macOS: Firefox unresponsive/freezes after locking screen




2 years ago
2 months ago


(Reporter: sebastian, Unassigned)



Firefox Tracking Flags

(firefox65 affected)


MacOS X 10.12.6 (16G1036) - MacBookPro

Firefox becomes unresponsive / laggy after the screen was locked for some time. The UI responds with a multiple second delay until the browser is restarted. At first I though this was somehow related to my specific device. But now after switching to a new device I have the same problem again.


* Lock the screen - I usually execute "Lock" via the Alfred3 prompt). Note that it's "Lock" and not "Sleep".

* Wait some time - Usually I notice the behavior after longer breaks. It needs to be at least long enough so that macOS askes for the password again.

Not sure if it's important, but some details about my setup:
* Two external displays
* Two Firefox windows - One on an external screen and another one on the MacBook
* Some pages that are always open: GMail, Google Calendar, IRCCloud, Slack, Hangouts, GitHub, Bugzilla
I think I observed this first with ~Firefox 55/56? But I'm not 100% sure.

Comment 2

2 years ago
I've experienced this too during my use of Firefox 57.0beta on macOS 10.12.6. My steps to reproduce are the same (I even lock my computer the same way with Alfred 3). And it only happens after being locked for a while (I want to say at least 15-20 minutes).

After unlocking my computer, when Firefox is focused, it appears entirely unresponsive. However, when I Cmd+Tab to a different application, then Firefox registers my action. For example, if I click on another tab to switch to it, nothing happens. When I Cmd+Tab to another app, then Firefox switches to the tab I clicked on. I have to restart the browser to get it back to a working state.

Comment 3

2 years ago
Experiencing the same issue on Firefox 58.0b13 on MacOS 10.12.6, and also use Alfred 3's lock command.

Comment 4

10 months ago
I have started experiencing exactly the same issue as described above, Firefox 61.0.2 on MacOs 10.12.6.
After locking the screen for a longer period(15-20 minuts seems rights), with Firefox as the application in focus, Firefox is unresponsible when unlocking. Only way to resolve it is to restart the application.

I lock the screen the ordinary way, not using Alfred3.
I can also reproduce this when switching users on macOS.  Same
experience as a_waal that leaving Firefox in focus for 15-20 minutes
reproduces it.

To me this looks like a graphics related bug because the browser
itself responds to interaction.
Could someone please use the profiler and create a session? This might give us the necessary information where all the CPU time is being spent.


1) Install the profiler addon:

2) Starting the profiler

3) Locking the screen for the necessary time to reproduce the problem

4) Unlock the screen and wait some seconds before capturing the profile (

If you can please share the profile with us, that would be great.

Comment 7

7 months ago
I have had this problem for about a year or so on a 2011 iMac. The problem seems worse on a new iMac Pro.

1) Use Firefox in one Mac user account
2) Login to a new user account (without logging out of the first)
3) Use Firefox in 2nd user account
4) Fast switch back to 1st user account
5) Firefox appears unresponsive. Technically, it actually is responsive. For example, if I left a Youtube page up, I can click where the video would be and I can hear it start playing, but visually you do not see anything. Likewise, I can cmd+T a new tab and start typing a URL, and even hit enter. Nothing will appear to happen. However, if I quit Firefox and restore the previous session, that new tab and website that I entered will load. So it's functioning, but there is just some kind of UI freeze going on.
6) Functionality can be immediately restored if I switch back to 2nd user account and immediately switch back to 1st user account (in other words, if I switch to the 1st user account twice).
7) Switching back to 2nd user account after Firefox functionality has been restored to 1st user account renders 2nd user account Firefox unresponsive.

I installed the Gecko Profiler and captured the above. But 10 minutes after clicking "Capture Profile" it says "We were unable to connect to the Gecko profiler add-on within thirty seconds. This might be because the profile is big or your machine is slower than usual. Still waiting..." Tried it a second time and same result.

Comment 8

6 months ago
Same problem on iMac (27-inch, Late 2012) running Mojave (all recent versions as released).

Easy to reproduce and doesn't seem related to sleep/locking the computer.

1. Use Firefox in one Mac user account
2. Allow computer to sleep ===> All normal on wakeup
3. Lock screen (^Command-Q) ===> All normal on unlock
4. Switch to a new user account
5. Switch back to original account
6. Firefox unresponsive. Cannot use Gecko Profiler.

Wondering if this is a different bug to the one originally raised and if so, should a new bug be raised?

Comment 9

5 months ago

I can confirm that this bug is replicable by switching users in Mojave.

Comment 10

5 months ago

Sorry, hit save too soon. 2018 MacBook Pro 15", Mojave with latest updates, Firefox Quantum 65.0. The lack of responsiveness happens every time I use fast switch between users.


4 months ago

I should note that this bug doesn’t reproduce when WebRender is
enabled (flip gfx.webrender.all in about:config to true and restart

Comment 12

4 months ago

(In reply to Andreas Tolfsen ⦗:ato⦘ from comment #11)

I should note that this bug doesn’t reproduce when WebRender is
enabled (flip gfx.webrender.all in about:config to true and restart

Thanks, does that require Nightly? Not listed in config for 65.0.1

Comment 13

2 months ago

Reproducible for me even with gfx.webrender.all enabled. Firefox cpu usage is >100% for a couple of minutes after waking up the Mac.

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