Great replacement for "Mozilla Archive Format, with MHT and Faithful Save."

But could you implement some optional compression like zip/gzip/deflate (or even xz/lzma or bzip2)? Nothing more complicated than putting the HTML file into a compressed container. Because currently the HTML files with base64 encoded images can be pretty big.

I guess the main problem may be to enable Firefox to open compressed HTML files. But maybe Mozilla likes to add such a feature if we open a bug request. Remember, Firefox already has code for decompressing zip/gzip/deflate, because that's needed in the HTTP code for compression. Mozilla has just to make use of that decompression code in the HTML code.

If Mozilla won't add support for opening compressed HTML, I still like to see an optional setting for ZIP compression. In that case the user has to care about decompressing the ZIP file before opening.