On Slackware 14.0 x86_64 with KDE - when doing "Browse to URL" the browser used is Konqueror.
I want to use Firefox. 
In Manage > Options > Misc. > Alternate Browser I have entered /usr/bin/firefox
But it still uses Konqueror
~/.pwsafe/pwsafe.cfg contains:        <AltBrowser>/usr/bin/firefox</AltBrowser>

Cheers,
Peter