Fix for Firefox Showing Blank Page When Downloading Files in Gmail
This issue might not help everybody, but if you are having problems with downloading files in Gmail because you get a blank screen, this page should help you out. The problem is because of an older version of the Tab Mix Plus extension, which you probably chose to "Make Compatible" for Firefox 3.
This is the screen you usually get when trying to download a file:
To fix this, open up Tab Mix Plus Options and choose the Links button at the top, and then the Edit button on this page.
Now delete these two items from the list:
Alternatively, you can install the Dev Build of Tab Mix Plus... here's a screenshot of the link so you'll know what to look for.