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This page describes the JavaScript Debugger as it appears before Firefox 52.

See what it looks like from Firefox 52 onwards.

The following are different ways to set a breakpoint within the JavaScript code in the debugger.

  • 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)

Each breakpoint is shown in two places in the debugger:

The screenshot below shows breakpoints at lines 20 and 28 of the file. The breakpoint at line 20 has been hit:

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