Open the debugger
There are three ways to open the debugger:
- Select "Debugger" from the Web Developer submenu in the Firefox Menu (or Tools menu if you display the menu bar or are on Mac OS X)
Press Ctrl + Shift + Z on Windows and Linux, or Cmd + Opt + Z on macOS (starting in Firefox 71; prior to Firefox 66, the letter in this shortcut was S).
- Press the menu button ( ), select "Developer", then "Debugger".