Make middle mouse button (paste) load URL in Firefox

Problem

Pasting a URL (middle-mouse button) into a Firefox browser window or tab does not cause the page to be opened.

Keywords

Firefox, middle-mouse button, paste, URL, tab, open, load.

Solution

Open about:config (by writing it in the location bar) and set middlemouse.contentLoadURL to true. Also check out Making Firefox Handle Multiline Pasted ("Broken") URLs.