It would be nice to have a utility to convert between web archive formats (Safari's .webarchive plist; MSIE's .mht MIME HTML; Firefox's web page, complete) until such time as Bug 7168, Bug 7169 and Bug 7211 are fixed.
Taking my own bug. I originally thought I could write this in a day, but there were more challenges to overcome than I initially thought. :) The current version uses Perl and will only work on Mac OS X since it uses (or will use) the PerlObjCBridge to create/extract .webarchive files (which are binary plists). I plan to have the script read each of the formats into an internal format-neutral data structure so that it can target any of the formats on output. Right now .webarchive to "web page, complete" is very close to working. Lessons learned from this project will undoubtedly help to implement the bugs noted in the Description above.