This page describes the JavaScript Debugger as it appears in Firefox 52 and above, in Firefox Nightly and Firefox Developer Edition.

To see what it's like in earlier versions of Firefox or in Firefox Beta and Release, see Debugger (before Firefox 52).

If you are getting this version of the Debugger and need to switch back to the old version, you can do so by visiting about:config and setting the "" preference to false.

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:

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Contributors to this page: wbamberg, rralian, Metonymy
Last updated by: wbamberg,