Comment 42 for bug 25830

OK. There are actually two separate issues here:

1) Have a way to set user preferences to handle a particular type as plaintext.
   I have the back end of this working in my tree (just reset the type on the
   channel to text/plain and punt the load back to the originating docshell).

2) Have a way for the user to select "view as text" from a helper app dialog
   that comes up for an unknown type. Here the problem is that the data is
   already being sent to dist at this point and the original docshell is no
   longer in the middle of a load -- it thinks it's done.

I have no idea how to solve #2 without completely rearchitecting all the helper
app stuff...