Which is totally fine on their own machine, but using a webfont to force ligatures on anyone viewing their website is just confusing as a reader.
No, I get it. I don't use them either because I find them confusing. I'm just telling you you missed out on what was a quite popular trend from a few years ago.
Lately my Firefox has been showing a ligature for "fi" in monospace code blocks, showing those two characters in the width of a single character. On every website with code blocks. It is mildly infuriating and I don't understand it.
Right-click the ligature text -> Inpsect. In the Inspector, on the right there is a tab called "Fonts" (to the right of "Rules", "Layout", etc). That will show you what font(s) Firefox used to render all the text in the selected element.
Using ligature fonts for programming became popular a few years ago. As in some people even use them in their editors.