If you are administering an Office 365 tenant, you might have tried to list the user profiles from the SharePoint admin center.

We can see a label showing "Total number of profiles" with a number just above the find textbox but there is no easy way to list them all.

I just discovered that if you search for the letter i and click the Find button, you will get almost all of them. A couple of profiles are missing but they are used internally and you probably shouldn't bother with them! The reason why the full list is returned when you search for I is because the internal account name is something like "i:0#.f|membership|accounting@YourDomain.com"