Actually, I think Opera has the same policy as Mozilla. If you reply to the reviewers (who are very responsive), they seem to let you minify as long as you show them the unminified sources.
Our extension (https://addons.opera.com/en/extensions/details/disconnect/) uses the minified versions of seven libraries, which are about half the size of the unminified versions. Why not give users a better experience by shaving a few seconds off the install time?