In the preferences, after selecting which file formats to open with Xee, you can't then go back and deselect many of them.

There have been some fixes for this made in the last version, but if there is no other program that can handle the file (as is the case with several of the formats Xee handles) there isn't much to be done.

Also, please don't start new threads for single issues, use the threads that are already there.