I think it's a feature, but it feels like a bug :
When in a tab you click to "export" a file that takes long time (configuration export from drupal website for example), and during that time you switch to another tab, and start typing something (in a webmail, i a forum post/comment) when the file window appear it gets the focus and what you were typing is replacing the filename (field that has the focus).
So i wanted to know if it's possible for firefox to prevent launching the system file saving windows and alerting the user that it's "ready" to save in the appropriate tab.