Welcome to the community! Could you please elaborate more on the issue you're seeing? When exactly does the video slow? Did you try using the other suggested browsers (Safari, Microsoft Edge, and Google Chrome) to see if it makes a difference? Also, try using incognito mode.
Also, try clearing the browser's cache and cookies and restarting the browser, try again. For more info, please check this link and see if that helps- https://adobe.ly/3URgWLl