Mozilla is testing a new feature called “Time Travel Debugging” in Firefox. This feature is for developers and is currently only available for the latest version of Firefox Nightly for Mac.
OMG! @FirefoxNightly just got time travel debugging. Best birthday present ever! 🎂 🦊
— Jason Laster (@jasonlaster11) July 26, 2018
The new Firefox Time Travel Debugging feature is a reimplementation of WebReplay, which was previously called in older versions of Firefox. According to Mozilla’s documentation, WebReplay allows Firefox content processes to “Replaying processes preserve all the same JS behavior, DOM structures, graphical updates, and most other behaviors that occurred while recording. The browser’s JS debugger can be used to inspect and control the replay.”
As such, this feature is very useful, allowing developers to document how complex pages are rendered and allowing developers to go back in time to see when and in which operations have failed.
Time Travel Debugging is part of Firefox’s Web Developer Tools, a set of site-oriented debugging utilities for developers that can be turned on and off by pressing F12 in each Firefox release.
The Time Travel Debugging feature is currently being tested, and it’s unclear when it will be added to the official release. Watch the Bugzilla page for the latest progress.