I did some more investigation today and it is indeed a site compat issue, and we should reach out. Here the explanation: There is nothing specific to Marionette that causes this behavior. But the website itself checks for `navigator.webdriver` and if that property is `true` it seems to exercise a different execution path compared to that one you can see when just opening the page in your browser. That is basically not what a site should do. Steps to reproduce: 1. Create a fresh profile and open Firefox 2. Change the preference `marionette.enabled` to `true` (it would enable Marionette after a restart) 3. Open https://bet365.com After step 3 you can observe the hang and freeze of Firefox during shutdown.
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I did some more investigation today and it is indeed a site compat issue, and we should reach out. Here the explanation: There is nothing specific to Marionette that causes this behavior. But the website itself checks for `navigator.webdriver` and if that property is `true` it seems to exercise a different execution path compared to that one you can see when just opening the page in your browser. That is something a site can do, but shouldn't cause the browser to freeze / hang. Steps to reproduce: 1. Create a fresh profile and open Firefox 2. Change the preference `marionette.enabled` to `true` (it would enable Marionette after a restart) 3. Open https://bet365.com After step 3 you can observe the hang and freeze of Firefox during shutdown.