Firefox helper applications

[Steven Heimann]

I just installed the feisty beta on my office desktop as it died and
6.10 seems so old now.

All seems to be working well except I am having some trouble with helper
applications in Firefox.  The problem is happening with all file types I
have tried but I will give the example of pdf's.

When I click on a link to a pdf file I am offered the application evince
to open the pdf file.  Because I prefer xpdf I select "other" as the
application to use and the navigate to xpdf using the "choose helper
application" window that pops up.  In the past after you had done this
once xpdf would always be offered as one of the available applications
without having to navigate through the file system.  

This no longer seems to happen and I have to navigate through the file
system every time.

How do I get Firefox to add applications to the list that pops up when
you first click on the link.

Thanks and regards
Steven