Any special reason you want to use the beta version and not the current release? You would normally only install the beta version if you are a tester and to test the next version or if you experience issues (bugs) that have been fixed in the Firefox 48 beta version. Keep in mind that the beta version receives an update twice a week. There is no guarantee that the beta version works without problems (crashes), so you will have to try it out yourself. It is advised to have the current release installed and install the beta version as a second version via a custom install in its own program folder. Also create a separate profile folder for each Firefox version. *http://kb.mozillazine.org/Profile_Manager