I'm happy to see you're looking to maximize the power of QuickBooks Online by multi-tasking in multiple companies! Currently, the system is designed to provide a consistent experience for the company you're signed in to. As your session is stored in your browser window, the best way to work on multiple accounts is by using a separate browser for each one (such as Chrome and Firefox). If you have any feedback about this, don't hesitate to submit it directly to our engineers.
Let me know if I can help with anything else.