"Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now" "Remove the Cookies": Tools > Options > Privacy > Cookies: "Show Cookies" --- Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Safe mode start window to disable all extensions. You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

I had this same problem, it pestered me for weeks. I noticed though, that it popped up when i went to my google homepage. I had installed a "virtual acquarium" application on my google homepage. Once I deleted this, the download problem went away. It is odd behavior though for a google page application.

After much frustration with trying to remove this message my comcast online rep discovered the solution. Bravo to him. Go to the Google home page and search for the aquarium.html "Gaget" and delete. Pooph!!! All gone. Hope this helps.