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Chris Peterson
YouTube page load is 5x slower in Firefox and Edge than in Chrome because YouTube's Polymer redesign relies on the deprecated Shadow DOM v0 API only implemented in Chrome. You can restore YouTube's faster pre-Polymer design with this Firefox extension:
Download YouTube Classic for Firefox. Restore Classic YouTube!
Mozilla Add-ons Mozilla Add-ons @mozamo
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Chris Peterson 23 Jul 18
Replying to @cpeterso
YouTube serves a Shadow DOM polyfill to Firefox and Edge that is, unsurprisingly, slower than Chrome's native implementation. On my laptop, initial page load takes 5 seconds with the polyfill vs 1 without. Subsequent page navigation perf is comparable.
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Chris Peterson 24 Jul 18
Replying to @cpeterso
To fix YouTube on Edge, you can install the Tampermonkey extension for Edge and this "YouTube Restore Classic" user script:
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Chris Peterson 25 Jul 18
Thank you to and for debugging. They see a smaller speed difference and say the bottleneck might be Polymer's polyfill for HTML Imports, not Shadow DOM. The latest version of Polymer, 3.0, uses ES6 Modules instead of HTML Imports.
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Chris Peterson 25 Jul 18
Replying to @cpeterso
The "5x difference" I measured (5 seconds versus 1 second) was the time to replace the gray placeholder boxes with content (comments and thumbnails) on my Mac and Windows laptops and 200 Mbps internet yesterday. Your results may vary depending on your computer and network speed.
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Chris Peterson 25 Jul 18
Replying to @cpeterso
Today I see the gray placeholder boxes for less than 1.5 seconds in Firefox but still over 5 seconds in Edge. won't let me benchmark a YouTube video page, but here is a test page I used:
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eric 24 Jul 18
Replying to @cpeterso
this is a weird move. If youtube loads slowly for someone they won't think it's their browser, but the site.
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Chris Peterson 24 Jul 18
Replying to @3_r1c
I assume Google has metrics showing that the Polymer redesign increases Firefox and Edge user engagement more than the slow polyfills hurt it. 🤷‍♂️ YouTube still serves the pre-Polymer design to IE11 by default so they could choose to serve it to Firefox and Edge too.
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Kayhan Suleman 24 Jul 18
Replying to @cpeterso @YouTube
I always wondered why works like ass on Edge even though the browser works great with everything else.
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Chris Peterson 24 Jul 18
Replying to @7kayhan @YouTube
To fix YouTube on Edge, you can install Tampermonkey extension for Edge plus this "YouTube Restore Classic" user script:
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just Dale ( so many gears to grind ) 24 Jul 18
Replying to @cpeterso
I admit that I am not 100% schooled on Polymer, but I have read this Tweet a number of times and I am really confused as to the statement. YouTube's new redesign relies on Polymer 1.0, by which is the only version that I know of that has a dependency on Shadow Dom v0?
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just Dale ( so many gears to grind ) 24 Jul 18
Replying to @cpeterso
From Polymer 2.0 docs > You can test Polymer 2.x by using the latest 1.0 version of webcomponentsjs, which is included as a bower dependency to Polymer 2.x. (webcomponentsjs versions prior to 1.0 support the older, v0 specifications for custom elements and shadow DOM.)
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