Comment 1 for bug 764424

It seems like (from my testing, and looking at the code). That this is all working as intended. Perhaps there is a small bit of a problem, in that .desktop files do not always contain all the mime types that an application can support (for example, certainly I can open a text file in firefox or libreoffice writer). As far as unity is concerned though this seems to be working fine (tested your cases, png to firefox, html to firefox, text to gedit, etc...)