I appreciate how helpful Mozilla's very own Multi-Account Containers add-on is working. When I type hangouts.google.com, it automatically opens up in Container B, which is what I want. When I type photos.google.com, it should open up in Container C, but it always opens up in a default (non-container) tab. When I click on the Multi-Account Containers button on my toolbar, and then choose Container C, I then type photos.google.com, and (as it should), photos.google.com opens in Container C, with Container C's cookies. I then click the Multi-Account Containers button, and I do see the check mark beside "Photos -- Google Photos" Always open in Container C. So how come when i open up a regular/default tab, photos.google.com doesn't convert into a Container C tab? I find this occurs only with photos.google.com. I don't have this problem with gmail.com (or mail.google.com). I don't have this problem, as I said above, with hangouts.google.com. I don't have this problem with any other sites/domains.