CanvasBlocker causes Firefox to allocate endless memory / memory leak when visiting leetcode.com

[piperun]

Unfortunately it doesn't always happen, but at times when you go to leetcode.com Firefox will warn "CanvasBlocker is slowing down this page" and suddenly the web browser becomes extremely unresponsive and you can see Firefox start allocating ram and using a lot of CPU power.

[MichailiK]

This is consistently reproducible on Proton Drive when uploading lots of images. Proton Drive seems to use the canvas API to locally generate a thumbnail/preview of uploaded images. During the generation of those thumbnails, the UI freezes for several seconds & leaks massive amounts of memory (to the point where the Linux kernel kills the browser due to the system running out of memory)

5 second profile i took through firefox's process manager: https://share.firefox.dev/4j8RNXo

kernel: oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=user.slice,mems_allowed=0,global_oom,task_memcg=/user.slice/user-1000.slice/user@1000.service/app.slice/app-gnome-librewolf-55046.scope,task=Isolated Web Co,pid=56264,uid=1000
kernel: Out of memory: Killed process 56264 (Isolated Web Co) total-vm:46950176kB, anon-rss:6929932kB, file-rss:108kB, shmem-rss:6749128kB, UID:1000 pgtables:75152kB oom_score_adj:100
kernel: oom_reaper: reaped process 56264 (Isolated Web Co), now anon-rss:160kB, file-rss:108kB, shmem-rss:184kB
systemd[2016]: app-gnome-librewolf-55046.scope: Failed with result 'oom-kill'.
systemd[2016]: app-gnome-librewolf-55046.scope: Consumed 33min 15.366s CPU time, 27.4G memory peak, 30.7G memory swap peak.