There are two ways to prevent the Firefox Download Manager from popping up.
props to Tekzilla for this tip.
1. In the Address Bar in Firefox, type “about:config”, without the quotes and no space before ‘config’
2. In the filter bar, type browser.download.manager.showwhenStarting
3. double click it, making sure the value turns from ‘true’ to ‘false’, and restart Firefox
Now, when you download a file, the download manager won’t pop up annoyingly. but remember to clear the download history, as that will still exist. To do so, click ‘Tools’, then ‘Downloads’, and ‘Clear’.
1. Go to ‘Tools’, then ‘Options’.
2. On the ‘General’ tab, uncheck the box next to ‘show the downloads window when downloading a file’, and click ‘ok’.