I have a similar thing but with profiling JS performance: if you profile a page in Chrome and then inspect the source code, it gives estimates of seconds spent per line of code. Firefox does not have this.

Being able to detect which function is the bottleneck is great, but being able to then figure out where the time is spent inside that function can be very enlightening too.

That‘s being worked on in Q1: https://news.ycombinator.com/item?id=15695910

This is also a big barrier for me using firefox in development, and pre-v57 Firefox used to have an extension for websockets that was nice, but its gone now with the new web extension APIs.