Unlike native right click menus, Firefox's don't let you type to select an option after right clicking. Right clicking text in Firefox also displays a different set of options from the standard textual right click menu which is pretty annoying if you're used to the standard one that appears in literally every other app (for instance, the native one lets you right click a misspelled word to select a correction).

This is one of those rare instances of "no, it's not just different, it's actually much worse".

Look Up "[selection]" constantly bugs me. I constantly use it to define words. I feel like there are others that come up periodically. It sounds pedantic, but it's enough of a pain point that I'm itching to switch browsers.

Speech. and the whole Services ecosystem.