In a multi-company tenant, the company name at the top is a button.
Click the company name (or badge) in the top bar to switch companies without going through My Settings. The badge colour and short name are set per company in Company Information → Company Badge, so a red "UK" and a blue "IE" tell you where you are at a glance; set them, because posting into the wrong company is a real error. Alt+Shift+W opens the current page in a new window, so you can have two companies side by side. Role centre cues for "my open orders" are per company; the Companies list (Tell Me: "companies") shows them all.
