The leave-open keyword is there and there is no activity for 6 months.
:svoisen, maybe it's time to close this bug?

"leave-open" was just here because we landed a testcase but no fix.

Having said that, though, it seems this is now WORKSFORME. I can load the testcase without any assertions/warnings being spammed and without any huge content.

I tested the attached testcase, as well as the in-tree version from comment 4, which is available here:
https://hg.mozilla.org/mozilla-central/raw-file/tip/layout/tables/crashtests/420242-1.xhtml

I'm using a 64-bit linux debug build. (Note: this bug technically has the platform field set to macOS, but I don't think it matters -- I suspect that's just where it was reported from, and there shouldn't be anything mac-specific about the layout code involved here. So I'm fine having tested on linux.)

--> WFM

Nightly fix range (determined by loading the attached testcase and looking for scrollbars to indicate huge content per comment 0):
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=10ea10d9993c9701e5525928257a589dea2c05d8&tochange=35c7be9c2db288d1d449e3cc586c4164d642c5fd

In that range, I would bet this was fixed by bug 1338108 (which is about arithmetic involving a zero width, which makes sense because margin:100% in the testcase probably leaves us with a zero width here).