Main body width very narrow in firefox with min font size > default font size

[ijackson]

Steps to reproduce

1. Start Firefox 91.5.0esr from Debian buster (other versions may work too) with HOME pointing to a fresh empty directory, to get a default profile.
2. Visit https://docs.rs/ureq/2.4.0/ureq/
3. In firefox, in a new tab or window, visit about:preferences, enter "font" in the search box, click on "Advanced...". Set "Minimum font size" to "18". Note that the default proportional font size is "16" or for mono, "12".
4. Observe that the main display column for the ureq docs is now absurdly narrow.

This is a regression (!)

This page https://docs.rs/vecdeque-stableix/1.0.0/vecdeque_stableix/ which was formatted a while ago with an older rustdoc, is fine.

Discussion

ISTM that this behaviour is undesirable and indeed unreasonable, and ought to be addressed in rustdoc. Particularly given that there is no UI in firefox which gives any kind of warning to the user who defines such an anomalous configuration.

I discovered this by visiting docs.rs and seeing misformatted docs. My browser configuration has not changed recently so I must have had this anomalous setting for some time, and by and large I find that most websites do work. I was only able to narrow down the reproducer by comparing different browser profiles and experimenting in about:config with font stuff (I had a hunch it might be relevant).

Screenshot

[ijackson]

@rustbot modify labels +T-rustdoc

[jsha]

Thanks for the report! Also being discussed at https://github.com/rust-lang/docs.rs/issues/1607, though we should move that conversation over here since this is a rustdoc issue rather than a docs.rs issue.

[jsha]

Actually, closing in favor of the other issue, which is now moved into the rust repo.