Rated 5 out of 5 stars

In reply to Mitch and Victonio: what you probably need is Save Complete integrated with Mozilla Archive Format (http://maf.mozdev.org/)!

You get:
* Integration with Ctrl+S
* Option to save in a single file (MAFF archive)

This review is for a previous version of the add-on (0.9b11).  This user has other reviews of this add-on.