In the past, there was the possibility to open a file with an arbitrary application on the PATH, even if it was not registered with a .desktop file. For example, I could open some movies with mplayer. This is no longer possible.

The possibility should be restored, or at least, the manual should tell about this, and tell how to work around this. There is an entry on the manual entitled "Open files with other applications" but there is no montion of the disappearance of this feature.