Great work! Some insights from FANG. Two more things are necessary to make this a game changer: 1. JS level API to record RNR traces and upload them along with error reports (this will be a new W3C standard). This will be a compelling reason to include Firefox into the automation toolchain and at that point compatibility with Firefox will be mandatory. 2. JS level virtualization or sandboxing. Right now we have the iframe-level sandboxing but this granularity is too coarse because modern web apps have become really big (think of O365). We need a way to fragmentize the JS execution context into smaller docker-like sandboxes and record RNR traces for them. Rationale: big subcomponents should be isolated from each other and have separate traces. As a side effect, this new VM API will enable us to do one cool trick.
Replay is in the user-research and validation phase and still quite experimental.
firefox-replay.com is a work in progress. We're still sorting out the best way to communicate record and replay debugging and the new use cases.
We'll share more on @firefoxDevTools when we have something to report.