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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.

When your code stops at a breakpoint, you can step through it using the four buttons on the left of the toolbar:

In order, the buttons are:

  • Play: run to the next breakpoint
  • Step over: advance to the next line in the same function.
  • Step into: advance to the next line in the function, unless on a function call, in which case enter the function being called
  • Step out: run to the end of the current function

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