Use Alt-F12 for toggling mouse mode on and off.

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As for scrolling in the Byobu, you'd need to enter scrollback mode, using F7.

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To enable mouse support by default for all these operations, add these lines to your ~/.byobu/profile.tmux:

    # Enable mouse support including scrolling

    set -g mouse on 

    # Versions prior to 2.1 may want this too:

    set -g mouse-utf8 on