I think pasting directly into “search and go” if you middle click in a browser is certifiably insane.

Maybe acceptable as “paste and go” if it recognizes the clipboard contents as a valid URL.

That’s not a problem with middle click paste, that’s a problem with Firefox. If you hit ctrl+v in Firefox does it search for whatever is in your clipboard? No, so why should it do that when you paste by mouse click?

No it doesn’t, because middle-click paste doesn’t interfere with any other function. There’s no downside to having it.

It is, but slower.