Yup, c:\apps\firefox\firefox.exe -no-remote -profile "C:\profiles\some-clean-profile" was my was-to-go method for testing various configurations. Knowing

Yup, c:\apps\firefox\firefox.exe -no-remote -profile "C:\profiles\some-clean-profile" was my was-to-go method for testing various configurations. Knowing about %USERPROFILE%\AppData\Roaming\Mozilla\Firefox\profiles.ini is also often helpful, eg. when you want to move certain profile folder.