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Investigate increase in First Visual Change and Speed Index for Firefox
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Description

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:

Screen Shot 2019-12-12 at 12.18.18 PM.png (736×1 px, 125 KB)

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

Event Timeline

I could see the same thing in WebPageTest (this is start render for Facebook):

71-facebook.jpg (1×1 px, 61 KB)

But not on all pages. The Obama page become faster(!) to render:

Screen Shot 2019-12-12 at 1.11.54 PM.png (1×1 px, 107 KB)

Let me create an upstream issue and ask.

This was reported upstream and they could reproduce. Only happens on Linux. However in the next release 72 the performance increased. There's nothing more that we can do about it.