for files of unknown size, the progress meter in the download window doesn't "cylon" like it does on windows on mac, try downloading a giant file. for me, I was trying with a 2.5 GB iso image. I'll attach a screen shot of mac, and one of windows. perhaps there is a missing "busy" rule in a pinstripe css for the download manager?

Sounds like a dupe of bug 304147 to me.

I'm using Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.1) Gecko/20061013 BonEcho/2.0

I agree with Gavin. *** This bug has been marked as a duplicate of 304147 ***