Automatic Groups domain account switching.
When you use multiple sign-in with groups.google.com using domain accounts, Groups doesn't always pick the right account. For example, if you visit groups.google.com/a/example.com/forum/, Groups may use the last domain account you were using, instead of your @example.com account. This can prevent you from seeing your organization's forums, and the switcher in the Groups UI is hidden behind a link and often redirects you away from the forum you were trying to visit. Groups Account Picker solves this by adding the "?authuser=N" query string to the Groups URL, where N is the account number you want to use for that group. This allows you to specify to Groups which account of yours to use. The current version defaults to two domain accounts, @chromium.org and @google.com, so it will only work for users with accounts in both of those domains (i.e., Chromium developers).