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The Performance Monitor collects performance data in realtime and puts it on a graph. It’s handy for detecting performance problems at a high-level. If your CPU, memory, DOM node count, or event listeners only go up while clicking around, you probably have a leak in your code.
I wasted a day on CSS selector performance to make a website load 2ms faster
It was at this point that the second penny dropped and I realised I’d been duped by a graphing misunderstanding and my own enthusiasm for improving…
There is not enough interest from the entire ecosystem to continue experimenting with JPEG XL — https://bugs.chromium.org/p/chromium/issues/detail?id=1178058#c84
I can't believe this, #Chrome is really removing the support for JPEG XL we've been waiting for years! 😡
I guess we'll (unfortunately) see a lot of turtles in Firefox soon, while browsing the Web with devtools open… 🐢
JUST LANDED in Firefox Nightly:
🐢!
Appears when the server response time for a request exceeds the recommended limit of 500 ms (adjustable in about:config).
Awesome dev work by @b4bomsy and planning by @digitarald & @janodvarko!
If you spot it and it helps, let us know!H
Dave Rupert 
Trys Mudford
