I'm using Firefox 35.0.1 on OS X, i.e. the latest version of Firefox and I can't find anything that is faster than "Show Source", click and drag (to highlight the desired url), copy, paste into url bar, and press enter.

I do not have any "Open" options on my right-click from "Show Source". From "Show Source" once I've highlighted the url, the only right-click options available are "Find Again", "Copy" (which I'm already doing, albeit from a keyboard shortcut), and "Select All".

If I try it from "Inspect Elements", I can expand the head tag, double-click to select the comment, click and drag to select the url, at which point my right-click only has the "Show DOM Properties" option available. But this has already taken longer than the above show source, then copy-paste, and go.