I don't think that bridging the connections is going to help you. If you have separate network connections - ADSL and Mobile - you can select which one to use. When bridged, the bridge will get a single IP address by DHCP either from the ADSL provider or from the Mobile provider; this will be the one that provides your internet connection, not both. You won't be getting an enhanced speed.
Even with separate un-bridged connections running, one connection will have priority and provide internet access.