User Agent: Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101 Firefox/38.0 Build ID: 20100101 Steps to reproduce: The Mozilla Suite and/or Firefox used to have UI that indicated the progress of uploads (such as form submissions with files) around 2002, see bug 24197. A later report about this feature not working correctly, possibly later or in a different place in the UI, was submitted in 2004 as bug 249338. This bug has now been closed as “won’t fix” and then reopened and reassigned from Core to SeaMonkey as Firefox doesn’t even show *down*load progress directly on tabs anymore. The problem remains that Firefox does indicate download progress (albeit in different places, namely, in Tools → Downloads or, under Windows, in the taskbar icon), but upload progress is not indicated. There is an add-on that handles this, Upload Progress, and I like it. But I think this is a core issue that should not be delegated to an add-on that may or may not be updated in the future (I don’t know, and I have no connection to the add-on other than recommending it to users of a simple site for internal file sharing that I developed some time ago). In essence, upload progress should be treated equal to download progress. Both should be indicated in the same place(s).

Isn't there any appropriate Component for Firefox UI? This bug was already WONTFIXed in "Core / HTTP" (as bug 249338), then REOPENED as a "SeaMonkey / UI Design" bug.

Yes, submitting it as a Firefox bug is what was suggested to me in bug 249338 comment 70 and that’s what I did. YF, are you sure you were right in making these reassignments? Also, I don’t specifically want to limit this to form submissions, an AJAX request could grow into a large upload-like transmission to the server as well.