Problem:
Although it is often a desired behavior, in some environments administrators would like to ensure Firefox profile data directory does not roam. This allows Firefox to run on multiple stations with the same user.
Symptoms:
You can notice this warning while logging into multiple sessions. 
Possible Solution(s):
Edit the profile.ini file located under
%userprofile%\Portability\AppData\Roaming\Mozilla\Firefox
with the following
[General]
StartWithLastProfile=0
[Profile0]
Name=default
IsRelative=0
Path=c:\temp\
The cache is then stored locally "c:\temp\" on the virtual desktop allowing multiple launches of Firefox.
Product: ProfileUnity
Product Version: N/A