Why does the address field just have "Go to a web site." instead of the URL of the page I'm viewing?
Ffx 11.0, XP-HEsp3 This seems to happen occasionally; at least once per day. I usually notice it soon after starting Ffx (but that's usually when I need to capture the URL.) The left end of the Location bar is green, with a faint square box that does nothing, and 'Go to a website' just disappears when I click it. The right end has the shortcut & history icons, which work. I can create a shortcut, and dig the url from that, but that's a pain, just to capture the URL for a reference. I used to just click, Ctl+c, click, Ctl+v, voila! Sigh.
Opaite Mbohovái (1)
Does that happen if a (JavaScript) link gets opened in a new window?
You can try to open a new tab (to prevent closing Firefox) and close (Ctrl+W) and restore (Ctrl+Shift+T) the not working tab t see if that brings the URL in the location bar.