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A Mozilla engineer says Google's redesign has made YouTube slower on Firefox and Edge.

Chris Peterson, the software community's technical program manager, tweeted on Tuesday that the video sharing site loads at a fifth of the speed on non-Chrome browsers due to its architecture, as first reported by Sofpedia.

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: https://t.co/F5uEn3iMLR — Chris Peterson (@cpeterso) July 24, 2018

"YouTube's Polymer redesign relies on the deprecated Shadow DOM v0 API only implemented in Chrome," he wrote.

"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."

Peterson suggested fixes for both Firefox -- Mozilla's browser -- and Microsoft's Edge that revert YouTube to a previous version using add-ons.

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He notes that YouTube "still serves the pre-Polymer design" to Microsoft's Internet Explorer 11, which launched in 2013 and has been replaced by Edge, and suggests that Google could have taken the same approach with Edge and Firefox.

Responding to Peterson's claim, a Google spokesperson said the company found that overall YouTube performance on Firefox is the same as it has been since the site redesign, based on the latest metrics,

It says that it's is always working to make YouTube faster, regardless of the browser you use, and will continue to do so. The company says it isn't perfect and recently fixed a bug that helps improve Firefox performance -- when it finds performance bugs impacting users for any browser, it fixes them.

"Mozilla employees are free to personally weigh in on discussions and share publicly their own hints and hacks that may make it easier for people to better utilize the web. As an open source company, we support the idea of giving people more information and access to tools that enhance the online experience which is valuable to all web users," a Mozilla spokesperson said in a statement.

"Mozilla continues to work on support for the standard Shadow DOM and Custom Elements APIs. We have been working with the YouTube team as they migrate to use of these standard APIs. The Firefox community maintains its focus on improving user-visible performance on all sites, including YouTube."

Neither Microsoft nor Peterson immediately responded to requests for comment.

In May, YouTube revealed that it has 1.8 billion registered viewers every month and previously said that 400 hours of video are uploaded to the site every minute -- so its performance is a vital factor in people's choice of browser.

Chrome is the most popular web browser and accounts for 59 percent of website usage, according to analytics firm StatCounter. Firefox accounts for 5 percent, while Edge has 2 percent.

Last weekend, Firefox added the ability to block autoplaying videos with audio to the Nightly test version of its browser.

On Tuesday, the latest version of Chrome expanded Google's fight against surveillance and security risks by showing a "not secure" warning for any HTTP website.

First published at 6:10 a.m. PDT on July 25.

Updated at 1:43 a.m. PT on July 26: Adds Google response, comments from Mozilla and corrects Peterson's title (he's not a Mozilla executive).

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