We got an SpeedIndex alert on Firefox on WebPageReplay earlier today.
The alerting graph looks like this:
Also looking at the First Visual change looks worrying:
Checking a little more in deep, it seems it correlates to a release:
Looks ok in Chrome though:
And I can see the same thing for all three URLS on enwiki on WebPageTest too:
At last checked my own instance. Same thing there, only visible on Firefox, not Chrome:
And nothing changed in TTFB. I wonder if we can see this in RUM too?
Note: I think we run different Firefox versions, both 68 and 69, so its not to a specific version.
Lets look into RUM and what has been going out.