I think it was around FF78 that they changed this behavior. Before that a single click just placed the cursor, double-click highlighted a word, and triple-click highlighted the entire address. This is the behavior for anything I click anywhere on my desktop (debian/mate) so I suspect what happened is the firefox devs decided to hard-code the behavior instead of letting the desktop handle it. I know there was a bug report for the issue which the devs repeatedly closed as won’t fix, at one point literally saying this was the way things worked in Windows and they were following that path for consistency across all operating systems, despite multiple examples given to show this was NOT the expected behavior on any Linux platform.
I’m not too surprised Chrome does this too, but it does make me wonder if Chrome following this path is the reason why the FF devs decided to copy it? Just because everyone else is doing it doesn’t mean that is the correct or expected behavior. ;-)