- Go the page you want in FireFox
- Scroll down to the bottom (or however much you want to capture)
- Tools > Web Developer > Developer Toolbar
- Type "screenshot --fullscreen <filename>.png" at the prompt at the bottom of the window
Probably don't embed them in this post as the screenshots are absolutely huge. For a look at the results, here's the recent Respect My Authoritah thread captured properly and uploaded to imgur.com. It may take a few seconds to print out bigger pages, and you might want to choose .jpg for them instead of .png to keep the size down as much as possible.
https://i.imgur.com/iyFdZCl.png
Happy archiving!