For the record, this is how lowercase l and uppercase I show up here: https://prnt.sc/258zzy0
I don't override the font, either HN or FireFox or Windows is picking a serif font. I assume you didn't explicitly choose a font where different things look the same, but if it rendered 'a' and 'Z' the same glyph, you wouldn't say that was a problem with the English alphabet or with case sensitivity, or anything other than bad font design, right?