Indeed. It's the user's browser and experience, it's not up to the website owner. But it's frustrating to get bug reports when a 3rd party extension is the problem, not the website. Many visitors will just bounce blaming the website too.
Many years ago I had performance issues with a site and the only reason I knew it was due to an extension is I dug into it with the dev tools and managed to identify Dashlane as the problem.