The current code (13bc494) had some last minute hacks to (a) remove an extraneous tab stop before the editor and (b) change the focus indicator for tabbing to the editor. I presume (a) is buggy (i.e. 3100903) because I can't tab to the code editor on Firefox. I'm not sure what the behaviour was before those 2 commits.
Here's a 30 second loom video comparing the two behaviours
Firefox 132.0 (64-bit) on Windows 11.