Rated 4 out of 5 stars
I installed this add-on in Firefox 3.6 and it worked very well. But after I uninstalled it, Firefox couldn't save web pages as before: it didn't create a folder beside the HTML file anymore! Fortunately, I had a backup of the Mozilla folder.
BTW, I'm in Linux (Debian Squeeze) and I'd also installed UnMHT in Firefox.
On Windows, without MAF installed, there is an option in the "Save As" dialog that allows you to choose whether you want to save a complete web page or only the HTML. The behavior you observed might be related to this choice; it is possible that on Linux this option is hidden by default, and you can see it only if you expand the "Save As" dialog to display all the options. Probably, by doing this, you could have reverted to the "Web page, complete" behavior without the need to restore your entire profile.
If you have other questions, or if this is not the problem and you want to help out in finding its source, you're welcome on the MAF mailing list, reachable through the extension's support page.