I joined Replay as a senior front-end dev a year ago. It's real, it works, we're building it, and it's genuinely life-changing as a developer :)
Not sure how well this would have fit into Firefox as a specific feature, given both the browser C++ runtime customizations and cloud wizardry needed to make this work. But kinda like Rust, it's a thing that spun out of Mozilla and has taken on a life of its own.
Obligatory sales pitch while I'm writing this:
The basic idea of Replay: Use our special browser to make a recording of your app, load the recording in our debugger, and you can pause at any point in the recording. In fact, you can add print statements to any line of code, and it will show you what it would have printed _every time that line of code ran_!
From there, you can jump to any of those print statement hits, and do typical step debugging and inspection of variables. So, it's the best of both worlds - you can use print statements and step debugging, together, at any point in time in the recording.
See https://replay.io/record-bugs for the getting started steps to use Replay, or drop by our Discord at https://replay.io/discord and ask questions.
Well it worked on firefox before, but only on macOS:
https://www.youtube.com/watch?v=rDq1AN1kSn4
https://web.archive.org/web/20210331133857/https://developer...
> But kinda like Rust, it's a thing that spun out of Mozilla and has taken on a life of its own.
It could has been a feature that make firefox the browsers for developers, instead it's a new paid subscription dev product.