Hi there,
Since you're also familiar with QuickBooks Desktop, it sounds like you're a loyal QuickBooks customer! That's awesome, and it's great that you've had a chance to explore all the options QuickBooks has to offer. I'd be happy to help with your question pertaining to the Online version.
QuickBooks Online doesn't have an "Open Windows" feature that's similar to that of QuickBooks Desktop. I can appreciate why you'd love to see this in the online version, as it helps to navigate through your account quickly and easily. Don't worry, though. There's a few ways to ensure that you're able to work on a report while also exploring other areas of your account at the same time.
When you select the report you'd like to run, right-click on the title and select to open in a new tab or window. Doing so means that you're able to toggle back and forth between your report and the rest of your account. If you're finding that you're going in and out of a report multiple times, you also have the option to save your changes by clicking Save Customization.
I realize this isn't quite the same as QuickBooks Desktop, but it's a workaround that's likely to help accomplish the same thing. I hope you get back on track with my suggestions. In the meantime, I'll pass along your feedback regarding the "Open Windows" feature to my product development contacts. We're always looking for ways to improve our products.
Have a great day.