If you're using Firefox 52 or later and need to switch back to the old Debugger, you can do so by visiting about:config and setting the "devtools.debugger.new-debugger-frontend" preference to
You can set a breakpoint in one of the following ways:
- in the source pane, click on the line number for the line you want to break at
- in the source pane, activate the context menu while on the line you want to break at, and select "Add breakpoint"
- in the source pane, highlight the line you want to break at and press Ctrl+B (Windows/Linux) or Command+B (Mac OS X)
The video below uses the context menu to set a breakpoint:
Each breakpoint is shown in two places in the debugger: