Tested on linux and windows. On windows (reproduced by several people). File dialog did not have focus by default. Clicking on dialog quite frequently did not enable the ok button. On linux (gnome 2.16), file dialog had focus by default with ok enabled. Periodically however the ok button would not be enabled on dialog appearance. In both cases, unfocusing and refocusing or minimising and unminimising browser usually corrected, but was rather confusing to the user who thought Firefox was not allowing them to download the file. Was unable to reproduce in 18.104.22.168 under linux.
Happened to me lots of times on Firefox 1.5.x (WinXP SP2). Still haven't downloaded any file on 2.0 so can't tell there. Happens absolutely always if I click to download many files, for example, by opening many download links in tabs. After I click OK on one file, "Save in" window opens, and I can see in the background the other download dialog with disabled OK. Sometimes when I choose the save location, the other download dialogs disappear, unfocusing and refocusing *Firefox window* makes them appear again.
Re: comment #2 - you said in background a disabled OK button. Apparently desired behaviour is for the *unfocused* dialog to have a disabled Ok. In this case a *focused* dialog has a disabled Ok - are you able to reproduce that in 1.5?
this should be marked as duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=353407 and changed this and https://bugzilla.mozilla.org/show_bug.cgi?id=357132 to depend on that, not reverse.
Was this fixed by the patch for bug 361909? (You'll need to test a recent Firefox 3 build to tell.)
This seems to be fixed (bug 361909). Please comment with steps to reproduce in Firefox 3 if you still see the problem.