We got alerts almost all over the place for Firefox with our new WebPageReplay setup but when switching between Firefox 70 and 71 but I also did some Firefox preferences changes around that time so I wan't 100% sure that the browser version had any impact.
It looks like this:
However I could see changes for WebPageTest too at the exact moment of the switch. A couple of pages got slower but the Obama page got faster.
I created an upstream issue to ask if they could pinpoint any changes https://bugzilla.mozilla.org/show_bug.cgi?id=1603404