Starting in version 52, Firefox includes a new debugger. The new debugger is currently enabled by default only in Firefox Developer Edition and Firefox Nightly. It's faster and more reliable than the old debugger, and provides a better foundation for future development.
However, it doesn't yet support all the features of the old debugger. This page lists features of the old debugger that are not yet supported in the new debugger.
Please note that we do intend to support most of these features in future releases, and this page will be updated accordingly.
If you need one of these features, you can switch back to the old Debugger by visiting about:config and setting the "devtools.debugger.new-debugger-frontend" preference to
The following features are not supported at all in the new debugger.
- Breaking on DOM events
- Highlighting and inspecting DOM nodes
- Examine, modify, and watch variables
- Black box a source
Search is partially supported: you can search for a file by name and search for a string within the current file. However, you can't:
- search across all files
- search for function definitions across all files
- jump to a particular line
- filter the variables displayed.