Jul 24 2023
@Novem_Linguae I experienced it again, at the same time you posted it. Tried isolating the root cause, but didn't have the time to do it thoroughly. All I found was that the issue disappeared when I used the Visual Editor as my default (instead of wikitext 2010). I assume the memory leak is either in wikitext2010 itself, or in its live preview feature, or in one of the scripts in my common.js that customize the wikitext 2010 editor and aren't compatible with the Visual Editor. Hope this helps you narrow it down.
Apr 7 2023
Add: it seems Wikimedia Commons is also affected. One Commons tab I opened earlier today is now taking 2.7GB.
Apr 5 2023
Experienced the same (https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#Memory_leaks). Browser is Edge Dev (112.0.1722.31) on macOS 13.2.1. I've found a 100% reproducible test case, which also works when I'm logged out of Wikipedia, and have all browser extensions disabled.