Unrelated : In this article double f, like in "affected" are rendered with the second f bigger than the first (both on firefox and chromium). I looked inside the css editor and the font seems to be ("Libre Baskerville", Georgia, Times, "Times New Roman", serif).

I guess this is probably to improve readability but it doesn't do this for other pairs of repeated letters.

It kind of sent me into a rabbit hole as I thought font were defined for a single letter only. I did a quick search and I couldn't find the rules which defined fonts. Is there some pattern matching for sequence of characters ? More importantly, when trying a new font how do we know that there aren't special cases like this ugly "ff" ?