Notably Ctrl+C/Ctrl+V operate on the clipboard, while selection and middle-click operate on (at least) selection1.
Which is my main use case for clicking in the location bar, copying the URL. So I appreciate that single-click selects all, so I can then copy with a keyboard shortcut.
I'm confused by your comment "when I want to copy it I have to triple-click anyway" -- I'm guessing you are on linux(?)... does triple-click or select alone automatically copy on Linux? (If select alone normally copies to clipboard, then I'd say it's a bug that it "looks selected" but hasn't copied to clipboard?)
This may be a thing where different behavior is appropriate for different OSes. Perhaps the FF devs who rejected the feature are also Linux users? I think FF wants to get market share beyond what can be achieved focusing on Linux users though.
I think they should make this configurable though, I can see both sides of it.
Ctrl+Click -> insert
CTRL+L would be the shortcut, but often I browse without my hand on the keyboard, just the trackpad or mouse.
You'd think after so long, I'd get used to the behavior and just single-click it. But apparently Pavlov would have me culled from his experiment :)