How can I make a screenshot of a web page that scrolls off the screen?

Firefox Add-ons

Fireshot – Windows only, ~~unfortunately.~~and I’m looking for an OS/X solution. I didn’t know Firefox add-ons could be OS specific.
Screen Capture Elite – Version 1.0.0.12 – the capture full page doesn’t seem to work on frames, but if you make the internal frame its own page it captured the full page. Works on OS/X.

Standalone