Firefox not unloading tabs on MacOS reliably ( fedia.io )

I currently have a puny 380 tabs open that consume 42GB RAM on my MBP '21 Max whatever (with 64GB total, shared with the GPU).

I have gone through most troubleshooting and it's clear that the unload mechanism isn't achieving it's goal (I mean, aside from an absolutely psycho amount of tabs I am hell-bent on having to "come back to later"). The reason that these tabs are open and have been loaded is that I've been transferring my other browser tabs over and setting up my Containers & Sidebar Panels, so each tab would have to be open within the last week.

Question: Most of resources I've found online lead me to believe that all I need is to modify browser.low_commit_space_threshold_mb. But it's nowhere to be found. about:config on MacOS is just returning an empty value and offers me to set it. Dare I? Would it actually work?

And yes, the browser.tabs.unloadOnLowMemory is set to true and browser.tabs.min_inactive_duration_before_unload is a default 600000 (which is in ms IIRC, so it's 10 minutes)

My main issue is that even manually triggering the Unload from about:unloads doesn't help the situation, and it can't be that all of the tabs are using WebRTC or are somehow considered to be active? Can it be a side-effect of Sidebery extension? Surely not? Many of the tabs list "Last Accessed" datetime between 3-9 days ago and still have the Base Weight of 0, so that part probably works, but Firefix decides not to unload them?

--
Random thought: It would really help if people wouldn't need to chase this. I assume that the way that MacOS handles RAM with it's swap and whole "memory pressure" is probably isn't the most simple thing to work around but unless I can fix this it'll be very difficult to consistently use, and I can imagine people less inclined to figure things out be easily turned off. And yes, I didn't use to have this problem with the other browser with just as mental number of tabs.

Day 9 of (finally) moving away from Chrome after Web Integrity API proposal is going swimmingly, as you can see.

Edits: formatting, added more details of troubleshooting

yoasif Mod , (edited )
@yoasif@fedia.io avatar

Question: Most of resources I've found online lead me to believe that all I need is to modify browser.low_commit_space_threshold_mb. But it's nowhere to be found. about:config on MacOS is just returning an empty value and offers me to set it. Dare I? Would it actually work?

You can always remove the edit if it breaks things catastrophically. Why not try it and see?

https://searchfox.org/mozilla-central/source/xpcom/base/AvailableMemoryWatcherMac.cpp leads me to believe that this functionality should work if you can trigger it.

I currently have a puny 380 tabs open that consume 42GB RAM on my MBP '21 Max whatever (with 64GB total, shared with the GPU).

This seems like the bigger problem.

If Firefox is using an unexpected amount of RAM, report a bug by following the steps below:

  1. Open about:memory in a new tab.
  2. Click Measure and save...
  3. Attach the memory report to a new bug
  4. Paste your about:support info (Click Copy text to clipboard) to your bug.

If you are experiencing a bug, the best way to ensure that something can be done about your bug is to report it in Bugzilla. This might seem a little bit intimidating for somebody who is new to bug reporting, but Mozillians are really nice!

If you prefer not to open a bug, you can instead reduce the number of content processes used by Firefox to a lower amount by going to about:config and changing dom.ipc.processCount.webIsolated to a lower number.

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