Firefox and ligatures under DOM renderer

[jerch]

Coming from #5155.

Recent Firefox versions changed 'ff' into a ligature repr, which causes issues in the DOM renderer and its char width measurement.

Repro:

• start demo
• switch to DOM renderer
• open demo in Firefox v130
• input 'abcdefgh' in terminal --> f gets rendered too wide

See #5155 (comment) for a possible quickfix. Problem of that quickfix is, that it will disable ligature support. A better fix would be to find a way to measure the char width independent of the ligature merging, e.g. by placing spans around the chars in the measure container.

Edit: Imho this still looks like a bug in ligature handling of firefox to me, as the 'ff' ligature breaks out of the monospace grid, while all others '==', '>=', ... stay within the correct width progression.

Edit2: The culprit causing this seems to be the "courier" font. If I remove it from font-family: "Fira Code", courier-new, courier, monospace, "Powerline Extra Symbols"; the broken ligature vanishs. Did MS change that old font recently?

Edit3: Nvm, my system uses "Courier" from the tex-packages, which includes ligatures. "Courier New" is the MS font, which does not have those ff ligatures. Btw thats a know issue with monospace fonts being not 100% monospace complicant ( e.g. ArtifexSoftware/urw-base35-fonts#31). Not sure if we can do anything here, it is yet again font madness.

[jerch]

@Tyriar Gonna close this issue unresolved - imho we cannot really do anything about this. Already tried the span idea from above in a playground branch, but the result is worse, it also disables all maybe wanted ligature behavior.

Only thing that can be done about it - the integrator/user may not use a font that exhibits this behavior. Imho we cannot give any helpful advice upfront beside that, as we dont know, which fonts are affected. (Also I have no clue, why only Firefox is affected, but not Chrome/Webkit/Safari).