Thanks, reply much appreciated. This is a different id because of the way Firefox works. I put the default 4* on this one ;) In answer to your questions as best I can:

* Firefox 68.8.0esr (up to date)
* Thanks for the downgrade info, I also found it in an obscure part of the Firefox info and can confirm LiveRecorder v1.6 still works fine on the same video where v2.0 fails.
* The simpler interface showing under the media after clicking the extension icon in the toolbar now only has two buttons, don't know if something is missing.
* You click record and it now counts up the Mb (a new feature).
* You click stop and get the error immediately which, tbh, looks like a code error referring to something undefined.
* It happens consistently, every single time, on all the several streams I have tried and every attempt. It also happens whether or not you have paused recording. For me at least, it looks to be a 100% failure where it isn't possible for it to work at all any more.
* The only thought I had was if Firefox changed something you now rely on between v68 and the latest (non-esr) version. LiveRecorder v2.0 might need a higher version than Firefox 68.
* Until I get to that on the Firefox esr channel, v1.6 works just fine, so thank you for a great extension. :)

While writing, just to point out in your documentation the FFMpeg command line you give to re-write the WebM file doesn't work (don't know if it did before). It doesn't re-write the timestamps with that simple command or even if you add options to ignore input timestamps and re-generate output timestamps. The lack of timestamps in the frames bacause of the Firefox bug confuses it and, on conversion, it writes a video with all 10,000 or whatever frames playing at 10,000 fps in 0s. Ooops! I have tried all the suggestions found by online search without success. However, HandBrake understands the WebM just fine, so you need to use that not FFMpeg (although I normally use FFMpeg too).