I am not able to reproduce the exact issue. Sequenced the latest build of Firefox on a system already having Reader 10.1.4, so that the reader plugins gets registered. On the sequencer the PDF is opening up in Firefox. The firefox package is then installed on a client system having Reader 10.1.4. When I open any PDF in firefox on the client, I always get the SaveAs dialog.
How are you sequencing Firefox. Are you making any customizations so that browser extensions work well. In this case browser is working within the virtual environment and might not be able to talk to local Reader.
We couldn't reproduce the exact same thing with 10.1.4 so I fear its a problem with the 10.1.0 version of Reader.
We are now looking to update Reader to version 11 with the last update to fix the issue's we are having. hopefully it works again with 11.
I would like to know if it ever worked correctly and in which build?
Did it work correctly prior to version 10.1.0 also?
To be honest no idea, we build a new KA network from the ground up (upgrading 1200 workplaces from XP to Win 7) and Reader 10 was the first version we used on that network.
Acrobat Reader 11 seems to be solving allot of the problems though.