Hello Danny.

That's a problem with Flash. I myself already complained to Google about their usage of Flash in Gmail, since there is absolutely no need for that in modern browsers, but they don't really listen to single costumers, do they?

In any case, that's not a Firefox bug, it's a bug with Flash. It's possible that it works ok with other browsers, but Flash is different for each browser, so...

But the drag and drop feature is HTML5 (afaik), and the locking of files does not happen when I upload files the "old" way (browse -> select file).

It is? Last I checked it wasn't. There's an easy way to see if it is: if you right-click the "suspect" area and you get the usual contextual menu, it's HTML, if it's some flash stuff that appears, it's flash.

If it's not flash, then it's a bug, most likely. But do try to replicate it on a clean profile (see how to manage profiles here) and the file the bug at bugzilla.mozilla.org, if it hasn't been filed before.

There is a flash in the subject line, as the uploader itself (progress bar) is flash. But I think the drag and drop ability is not flash (I may be wrong, I am making an educated guess).

In the gmail blog it is claimed to be supported only in FF 3.6 - which is when the drag and drop ability was introduced.

Well, I can't look into it at the moment, but it's possible that it's a Firefox bug and not a Flash bug, if it uses the drag and drop HTML function.