I use the latest official Mozilla Firefox version and extract the portable version.
It runs perfectly outside the sandbox, and is run with the following cmd line parametres: -private -no-remote -profile "profile1"
When I start it like this:
"C:\Program Files\Sandboxie\Start.exe" "C:\Program Files\Firefox_portable\firefox.exe" -private -no-remote -profile "profile1"
it will give me an error box telling me that "Your Firefox profile is not available" (Free translated, I don't know what it writes in English).
Windows 7 ultimate 32bit, Sandboxie v.5.30