[barrettondricka]

There is "SingleFile"[0][1] and a tool called "Monolith"[2]. Of course Ctrl+S works quite well too.

[0]: https://addons.mozilla.org/en-US/firefox/addon/single-file/

[1]: https://addons.mozilla.org/en-US/firefox/addon/singlefilez/

[2]: https://github.com/Y2Z/monolith

They all have ShowHNs with (probably) many more alternatives in the comments.