The reason I used Firefox daily many years ago was because of the Firebug debugger. The more complicated pages became the more important it was to have an excellent debugger/browser combination. Chrome launched with a solid solution and has kept pushing but it isn't nearly as good as debuggers in other platforms. All the browsers are all pretty bad at debugging the lower level stuff like graphics. What is the GPU doing? Why was rendering this last frame slow? What is happening inside of this WASM blob? Is transferring information in and out of this worker the problem or was it the worker itself?
If Firefox had an amazing debugger I would use it every day. I focus on graphics so this is where my mind is at but there are plenty of things that would benefit everyone like a better memory profiler or maybe being better about explaining to users how to fix issues. Chrome's Lighthouse might focus on how google works but it will also provide solid tips for how to make most websites better. Sure it might be wrong if you really know your stuff but it is also a great place to learn if you don't think you know it all.
I work for PaperlessPost.com, and for our Flyer product we export mp4s from ffmpeg compiled to WASM, which is similar to ffmpeg.js but optimized for our use case which sounds similar. We have this WebAssembly method working well but iOS 15 (and the other major browsers) now support MediaExporter which might be a better way to go if you have something else to convert these files. This becomes and issue because you can't control the format MediaRecorder is recording to but the management of memory, the image quality, the compression, the performance hit will be more ideal than these other methods. OMGgif is very slow and will produce large files or very bad looking ones. Keep in mind that GIFs limit the colors so something that looks nice on the screen might not look the same after it is saved. The other thing to look out for is the WebCodecs APIs which should be the ultimate way to handle all of this in the future but it is only working in Chrome I think https://github.com/w3c/webcodecs
If Firefox had an amazing debugger I would use it every day. I focus on graphics so this is where my mind is at but there are plenty of things that would benefit everyone like a better memory profiler or maybe being better about explaining to users how to fix issues. Chrome's Lighthouse might focus on how google works but it will also provide solid tips for how to make most websites better. Sure it might be wrong if you really know your stuff but it is also a great place to learn if you don't think you know it all.