I don't use breakpoints much, as most of the functions I'm debugging are small, so debugOnce or debug are usually pretty efficient.
Disclaimers aside, what you're describing should work, with one caveat: You have to run the script with "Source", not by sending it line-by-line to the console, e.g. by highlighting and running. If it's working correctly and you're debugging a function, a red dot will show up to it in the Environment pane.