Portable Windows apps can be run from any location without installation.
Firefox checks for other instances of Firefox before it runs. If it detects another Firefox running then it just spawns a window. Occasionally you want to run the browser as though it was on the remote machine possibly through SSH x forward. You have two choices close all Firefox instances locally or run Firefox on the remote machine with the following switch -no-remote or set the MOZ_NO_REMOTE=1 environment variable.