Why this happens?

When I load and run eg Firebox, the page just close and appears on my taskbar as an icon. This happens on most softwares. This only appears at the initial start.

Any advice appreciated. Thanks.

First possibility: someone got to your pc and pranked you by changing the shortcuts' property to 'Run as Minimized'.

Second possibility: Coincidence the software in question do run as minimized at startup. Altho Firefox would not normally run as minimized.