A former Microsoft intern has revealed details of a YouTube incident that has convinced some Edge browser engineers that Google added code to purposely break compatibility. In a post on Hacker News, Joshua Bakita, a former software engineering intern at Microsoft, lays out details and claims about an incident earlier this year. Microsoft has since announced the company is moving from the EdgeHTML rendering engine to the open source Chromium project for its Edge browser.

Bakita explains that “one of the reasons we [Microsoft] decided to end EdgeHTML was because Google kept making changes to its sites that broke other browsers, and we couldn’t keep up.” Bakita claims that Google added a “hidden empty div over YouTube videos” that affected Microsoft’s hardware acceleration for videos. “Prior to that, our fairly state-of-the-art video acceleration put us well ahead of Chrome on video playback time on battery, but almost the instant they broke things on YouTube, they started advertising Chrome’s dominance over Edge on video-watching battery life.”

The claims are surprising if they’re genuine, and they come months after a Mozilla program manager claimed a separate YouTube redesign made the site “5x slower in Firefox and Edge.” That incident led Edge, Safari, and Firefox users to revert to scripts to improve the YouTube experience. Google was also at the center of claims it intentionally blocked access to Google Maps for Windows Phone users years ago.

“Now while I’m not sure I’m convinced that YouTube was changed intentionally to slow Edge, many of my co-workers are quite convinced,” says Bakita in his post on the empty element issue. “To add to this all, when we asked, YouTube turned down our request to remove the hidden empty div and did not elaborate further.”

Google disputes Bakita’s claims, and says the YouTube blank div was merely a bug that was fixed after it was reported. “YouTube does not add code designed to defeat optimizations in other browsers, and works quickly to fix bugs when they’re discovered,” says a YouTube spokesperson in a statement to The Verge. “We regularly engage with other browser vendors through standards bodies, the Web Platform Tests project, the open-source Chromium project and more to improve browser interoperability.”

At the heart of these issues is an ongoing battle for the web. It’s clear Microsoft has struggled to keep up with the pace of changes at Google, and many of the search giant’s engineers play important roles in pushing web technologies and standards forwards. Google is often the first to adopt these changes as a result, leaving other web developers to play catch up.

It’s an issue that’s resulted in a number of Chrome-only sites from Google, as the company continues to adopt and push web standards forwards. Whether that’s Google’s fault for pushing too fast, or Mozilla / Microsoft’s fault for being too slow is still open for debate.

Microsoft isn’t commenting on the specific claims made by a former intern, and the company tells The Verge that “Google has been a helpful partner and we look forward to the journey as we work on the future of Microsoft Edge.”