.cfs is the official PFM extension, so yes, it will work with browser too.
To avoid questions why CFS, not PFM.
I was though that it would be good to create universal extension (
Common
File exten
Sion) so any applications can exchange files. As windows phone prevents us from being good users
we can do something to make our live better. For example any app can register to cfs and later wait for files.
For example one app receive only .doc files. So other app can rename "example.doc" to "example.doc.cfs" and ask phone to open it, other app when receive such file will remove .cfs and check for original extension and if it suits this app, save it or do whatever its want .
But unfortunately I did not found developers who interested in this idea.