Another problem:

In user-mimetypes.list we have mapped
and xrefs also maps .dvi to Evince Debian. However, dvi files (device independent LATEX output) are invariably opened by native evince, which unfortunately cannot handle them although it has dvi files under its mimetype declarations.

I even tried to enforce dbus-switchboard by entries
in defaults.list and uri-action-defaults.list, respectively. But to no avail, despite running
and rebooting.

Indeed, the entry
in /usr/share/applications/mimeinfo.cache remains and only evince gets started.

I guess I could manually modify the files of the evince package to no longer refer to x-dvi, but above all I would like to understand how I can actually use dbus-switchboard to determine which program handles what, even when several packages could do the same. I'm really lost in this mime maze! It's not that I need mime support for this file format so urgently - I used it to learn about mime and dbus-switchboard, but are now driven to the conclusion that this is totally beyond me.

qole, I attach a (gzipped) sample dvi file, in case you want to reproduce all this.

EDIT: Just noticed that /usr/share/applications/mimeinfo.cache had a time stamp from some 2 weeks ago. Just deleting the dvi related entries there solved the problem that all the other configurations didn't have any effect for that mime-type. I just wonder who is in charge of that cache as update-mime-database doesn't update it? This is like fighting a hydra!

EDIT2: Turns out that that solved my problems only partially: Local dvi files now open with Evince Debian with microB, but when opened on the web, microB says "application/x-dvi" and still only offers to save, and not to open with dbus-switchboard, despite having made entries for that type in defaults.list and uri-action-defaults.list. I now also need to supply a line
application/x-dvi=hildon-dbus-switchboard.desktop in /usr/share/applications/mimeinfo.cache. While it now works, this is completely nuts! What am I missing here? Why was that not necessary with application/postscript??