Given we understand the difference between an open source application and a closed source application that uses open source libraries... Then I can answer. If

Given we understand the difference between an open source application and a closed source application that uses open source libraries... Then I can answer. If Chrome etc were actually open source then the vendors would have less control of the browsers and users would have more control. End users could then build Chrome themselves. Since these browsers are in reality proprietary it would make little difference to end users vs vendors level of control if they used 0% code from open source projects rather than 99% as they do at the moment. No one but Google can build Chrome either way. So we broadly agree that there is nothing amazing about the current situation. I however claim that if these browsers were Foss this would be different. --- Yes I am aware of Chromium. But Chromium is not Chrome. For example Netflix supports Chrome and blocks Chromium.