Day 537. The #Azure Portal setting for startup directory applies to your whole Microsoft Account and not just the browser you are currently in. Which is kind of stupid, because if you have multiple browsers set up for multiple Azure tenants, Azure will per default always log you into the same Azure tenant, regardless of your work environment.
@azureshit Yes, this is do stupid. I use separate bookmarks for each tenant/directory just to work around this.
@saxx @azureshit jap, bookmarks is the solution.