The download dialog couldn't pop up when click to download the second time

Bug detailed description:
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Image: created on 01/31/2008

If click some hyperlink to download some files the first time,it could work well and the downloads management dialog box pops up(Perhaps it shouldn't be called dialog because it fills the whole screen).But if don't close the download dialog and click the icon on the topleft which seems like a house,you will enter desktop.Under this condition,you can click the house icon again or click the icon of firefox to return to firefox,and you will still got previous firefox,but the download dialog won't be seen.As we know,if we use windows or linux,this dialog should stay in status bar,but now we couldn't see it and if we download some files again,the download dialog won't pop up again and we can't see the process when it is downloading.

Reproduce steps:
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1. Launch midbrowser.
2. Download something,for example,an mp3 file.
3. Don't close the download dialog and click the house icon on the topleft.
4. Return to previous firefox via click the house icon or firefox icon.
5. We couldn't see the download dialog again and in this step,we download some files the second time.
6. The download dialog still doesn't come up and we couldn't see the process.

Current result:
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     The download dialog couldn't pop up when click to download the second time.

Expected result:
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     The download dialog should pop up when click to download the second time.It is to say,if we don't close the download dialog and we also want to continue downloading,the download dialog should pop up for us to see the whole process.

Basic root-causing log:
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