Problem with file-type association

[Séamas Ó Brógáin]

Since I upgraded to Ubuntu 11.04 I have experienced some problems with
file-type association.

I wish to associate .txt and .nam with a text editor and .sfd with
Fontforge (font editor). If I use the normal method of selecting a
representative file and opening Properties > Open with, all three types
are changed. If I use this method to associate .sfd with Fontforge, all
plain-text files are associated with Fontforge.

I understand that the association is stored in
~/.local/share/applications/mimeapps.list; but when I look in that file
I see that for Fontforge the association created by the normal method is
described as “text/plain”––in other words, it is reading the “filetype,”
which is indeed plain text, not the file-name extension.

Is there a way in which to explicitly link a specified file-name
extensions with a selected application?