2004564 - Constantly growing `heap-unclassified` and memory usage on Debian Sid

Status: UNCONFIRMED

(Core :: Performance: Memory, defect)

Description

[[:yardrat]]

Attachment: memory-report.json.gz exported from `about:memory`

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:146.0) Gecko/20100101 Firefox/146.0

Steps to reproduce:

Debug my company's front-end website locally.

It's Vue3, and hosted at localhost:5173 locally.

I launched firefox in both normal mode and troubleshoot mode, and the issue persists

I tried some other casual websites (i.e., google, bing, etc.), the issue is not that serious, but persists

I'm sorry but I can't share the website source code due my company's confidence codes, but the issue is mainly about the main process. Thanks for your efforts to build firefox. :)

Actual results:

The memory grows constantly, and consumed all of my 16GB memory. I've got no solution but to power-off and reboot.

I checked about:memory and about:process, and found that most memory usage are due to the main process, instead of the specified process for my website.

The peak consumption can be up to my entire 16GB memory, and the heap-unclassified can take up to 90%.

I've also tried other casual websites, and also spotted heap-unclassified issue. This time not that serious (about 30% to 40%), but it persists.

Expected results:

My company's front-end page shouldn't have used that much memory, since my fellow workers don't report such bug on other environments.

Also, firefox shouldn't even consume such an abundant of memory (approximately 8GB to 10GB) for a single website.

Comment 1

[[:yardrat]]

Here's some follow-up info about my OS and firefox build.

1. OS
   PRETTY_NAME="Debian GNU/Linux forky/sid"
   NAME="Debian GNU/Linux"
   VERSION_CODENAME=forky
   ID=debian
   HOME_URL="https://www.debian.org/"
   SUPPORT_URL="https://www.debian.org/support"
   BUG_REPORT_URL="https://bugs.debian.org/"
2. Linux kernel
   6.17.10+deb14-amd64
3. firefox version
   Mozilla Firefox 146.0b9
4. Where I got my firefox build (APT source)
   Types: deb
   URIs: https://packages.mozilla.org/apt/
   Suites: mozilla
   Components: main
   Signed-By: /etc/apt/keyrings/packages.mozilla.org.asc

Comment 2

[[:yardrat]]

Attachment: `about:support` info

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Performance: Memory' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 4

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:jlink, could you have a look please?

For more information, please visit BugBot documentation.

Comment 5

[lists]

I have the same issue. I can reproduce it with only one tab open: about:memory

Version: 146.0.1 (64-bit)
Debian testing
kernel: 6.17.12+deb14-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.17.12-1 (2025-12-14) x86_64 GNU/Linux

The process uses all memory until the oom killer removes the process, excerpt from dmesg:

[761252.341790] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-1000.slice/session-2.scope,task=firefox-bin,pid=355916,uid=1000
[761252.342308] Out of memory: Killed process 355916 (firefox-bin) total-vm:26584216kB, anon-rss:4883244kB, file-rss:3272kB, shmem-rss:408kB, UID:1000 pgtables:45948kB oom_score_adj:0
[761253.299846] systemd-journald[364]: Under memory pressure, flushing caches.

A few seconds running and only the settings tab and about:memory tab open:

Total resident memory (approximate) -- 2,013.75 MB
Main Process (pid 357620)
Explicit Allocations

2,105.40 MB (100.0%) -- explicit
├──1,936.76 MB (91.99%) ── heap-unclassified
├─────63.67 MB (03.02%) ++ (31 tiny)
├─────53.78 MB (02.55%) -- js-non-window
│     ├──32.13 MB (01.53%) -- zones
│     │  ├──29.05 MB (01.38%) ++ zone(0x7efd7898a000)
│     │  └───3.08 MB (00.15%) ++ (2 tiny)
│     └──21.65 MB (01.03%) ++ (4 tiny)
├─────27.27 MB (01.30%) ++ window-objects
└─────23.92 MB (01.14%) ++ storage

Other Measurements

1,342.97 MB (100.0%) -- decommitted
├──1,335.86 MB (99.47%) -- heap
│  ├──1,103.98 MB (82.20%) ── decommitted
│  └────231.87 MB (17.27%) -- unused-pages
│       ├──174.70 MB (13.01%) ── fresh
│       └───57.17 MB (04.26%) ── madvised
└──────7.11 MB (00.53%) ++ (2 tiny)

All extensions are disabled and the issue still persists. The issue goes away with a new (=empty) profile.

Comment 6

[lists]

Is there anything I can do to help? Provide logs or something?

It's 100% reproducible here. Just starting Firefox with the about:memory tab open and immediately closing it will eat up all the memory and the OOM killer will kill the process in approx. 1min. Leaving the window open will of course do the same. But it's strange that closing the window keep the process running in the background, and still eating up all RAM.