We'll learn how to use mouse mode in tmux, including enable mouse control for resizing, scrolling and selecting panes. We'll also set keybindings in our tmux configuration to control mouse mode.
Not sure what's different about your mac environment than mine, but these settings don't work:
bind R source-file ~/.tmux.conf
bind m set -g mouse on bind M set -g mouse off
Lowercase and uppercase m are already in use by the default tmux configuration; from the man page:
m Mark the current pane (see select-pane -m). M Clear the marked pane.