[CentOS] semi-OT: t-bird mime type on .pdf attachment is wrong

I was sending my manager a copy of a form, and attached it (not inline),
using -t-bird, and he complains it didn't want to open. Looking at the
message source, t-bird had decided that the mime type was all/allfiles,
though the name ended in .pdf. I've searched via the config editor, and
I've been googling, and not finding anything. (I just *adore* the current
google: I have +"all/allfiles" in the search terms, and in the para it
displays on a hit I see "all somethingorother", with the word "all"
bolded....)

Anyone got ideas? I've looked in
.thunderbird/<blah>.default/mime_types.rdf, and everything looks good in
there.

       mark