Hi, Robert -- I'm experiencing the identical problem you were (are?) having when opening Firefox on my Mac. I wish I had an answer for you...Has anyone helped you to solve it yet?

My googling hasn't come across many mentions of this issue, but I'm glad not to be the lone ranger!

Thanks, Lolly

Lolly,

I don't have that problem any longer. I solved it by closing the tab opened in Firefox to the Adobe flash download page. (I usually have many tabs open in my browser).

It is either that (still having a tab with the download page open) or a problem with the Download Manager trying to resume or restart an unfinished download.

For the first, check all open tabs as posted above. For the second you can try to clear the Download Manger window (Tools > Downloads) or delete downloads.sqlite the Firefox Profile Folder if deleting the download history didn't work.

See also Delete browsing, search and download history on Firefox