Using Firefox Nightly build 20221002212226 with
privacy.resistFingerprinting.letterboxing:true, if the browser window has a width less than ~800px, the toolbars and content window can get cut off along the right edge (e.g. the main menu hamburger button can get cut off). The issue appears to occur under a variety of condition. It does appear to be affected by the content of the displayed page. One reliable reproduction I've used:
- Open a new browser window and resize it to 800px wide.
- Navigate to https://git-scm.com/docs/git-config
- Find in page (Ctrl+F) "safe."
When the "." of "safe." is entered in the search box, letterboxing appears along the left side of the browser window and overflow occurs along the right, cutting off the main menu button and the right edge of the page content.
I'm able to reproduce the issue on Sway and Mutter using either a native Wayland window or XWayland window. Bisection with
mozregression --pref privacy.resistFingerprinting.letterboxing:true --arg https://git-scm.com/docs/git-config gives pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=dd74d4159c5dfa4307f663df24cf64766a4d5781&tochange=61cde6b6f2737eee00c49fb75390aff3d814f677 suggesting this was regressed by Bug 1789168.