What does MouselookHandler do?
MouselookHandler can lock you into mouselook, so you don't have to press the right mouse button constantly. It also allows rebinding your left and right mouse buttons to something new, while mouselook is enabled. By default, it rebinds them to strafe left and right.
You can set up custom conditions that control when mouselook should be toggled as well. For example, to have mouselook auto-enabled while moving.
Access the in-game configuration panel using the /mouselookhandler or /mh chat command.