attached files and Thunderbird 3.0

[Vu Pham]

I have several emails from different people with attached PDF files.
For some of these emails, when I double-click the attached files, I am 
shown the otpions to save or to open ( view ). Some others only show me 
the option to save, NOT to open. For these emails I have to save the 
attached files somewhere before I can see them.

These attached are all PDF files. Anybody experience this problem ?

Thanks,
Vu