Consistent but random stutter diagnosis

My Firefox installation constantly stutters at consistent but ultimately apparently random intervals. I recorded whilst quickly switching between tabs, because that usually induces it.

about:processes displays 100% extension usage at these times, but I don’t know how to ascertain which extension, because it doesn’t provide a process tree. displays the same — merely “WebExtensions” without any child processes.

I’m not using, as #nightly would indicate (there’s merely no #Firefox category, and the category is mandatory). I’m using (on cpe:/o:opensuse:tumbleweed:20240315).

I’ve recorded solely from the WebExtensions thread in about:processes for 5 seconds.