People expect websites to work regardless of the device or browser they are using. When a site works in one browser but not another, that is most likely a web compatibility bug that we want to know about. Users can report issues using a menu item in Firefox for Android Beta.
Downloaded files are no longer deleted when uninstalling Firefox (note that this only applies to files downloaded after this update)
TLS certificates issued by Symantec are no longer trusted by Firefox. Website operators are strongly encouraged to replace any remaining Symantec TLS certificates as soon as possible, before Firefox 64 final release on December 11.