Forcing users to use an extension isn't great as a workaround for this, if we plan to work around it at all, since it will only affect the tiny minority of users who a) use Firefox and b) install the extension. If a Firefox extension is written, it would be most sensible to have it just generically provide an upload progress indicator for all uploads.
Well, I mixed two things here: the general progress indicator thing, and the specific need for a good upload client for mediawiki. Both could be addressed by firefox ad-ons, btu you are right: for the progress indication, it should be generic, for any file upload. A mediawiki upload should be specific and provide more functionality besides picking multiple files and uploading them. Most importantly, it has to provide a way to provide the basic information about license, source and authorship. Programs for this exist, I was just thinking that a firefox ad-on would be simpler to deploy and maintain that a standalone program, and people would be more likely to iunstall and use it.
-- daniel