User interface of focused application is covered by another application's new window in Xfce

A few applications start slowly (especially by older hardware) and I think it would be productive, if you could do something else – e.g. read mail – by the computer meanwhile. Especially restoring last session in Xfce may open a lot of applications and even more windows you have to wait. Window Manager settings include an option not to give focus to newly created windows, but it does not help much, if windows keep popping up covering the user interface of the application you are using. Gnome and KDE handle this case much better.

That is not the whole issue: Also dialogs of background applications may pop up. This is also problem in Gnome; see Bug #67476.

By the way many applications can be started minimized by kstart --iconify. A notable exception is Firefox, see Bug #211533.

In summary:

An application may never interrupt user using another application. More specifically, an application may never steal focus or pop up a window while user is using another application, except when explicitly requested to do so by user (usually when starting an application from Applications menu or raising it from task list etc.). Even then user may choose to cancel the request by using another application, e.g. by typing in a text editor or clicking on an application. User should be informed about a new window opened in background by e.g. blinking respective item in task list or system tray.

Bug is present in Xubuntu 8.04.