Microsoft on Thursday began blocking rival browsers and search providers from using Windows 10's Cortana search box, the operating system's prime search real estate.

"To ensure we can deliver the integrated search experience designed for Windows 10, Microsoft Edge will be the only browser that will launch when you search from the Cortana box," said Ryan Gavin, general manager of search marketing, in a post to a Microsoft company blog.

The Cortana search box -- at the lower left of the Windows 10 desktop -- relies on Microsoft's Bing search engine.

Gavin defended the move by saying that "some software programs circumvent the design of Windows 10 and redirect you to search providers that were not designed to work with Cortana." When that happens, Gavin said, users get a "compromised experience that is less reliable and predictable."

While Gavin didn't name names, Mozilla's Firefox modified Windows 10 so that when that browser was made the operating system's default, Firefox's selected search provider generated results from in-Cortana queries, with the ensuing pages appearing in Firefox, not Edge. Other browsers, such as Google's Chrome, did not go that far, but third-party extensions available in the Chrome Web Store did.

The changes won't affect the basic functionality of non-Microsoft browsers, Gavin pledged: Chrome, Firefox, Opera and others will continue to work as before and will still default to their set search providers when queries are made from within those browsers.

But the Cortana search box is now Bing-and-Edge-only territory.

Microsoft has good reason for staking out Cortana as its exclusive turf, and not simply because of the disruption to Cortana's delivery of personalized results that Gavin mentioned. The Redmond, Wash., company has bet that Windows 10 will generate revenue outside the traditional licensing fees that OEMs (original equipment manufacturers) pay.

Not only does Microsoft want to push users toward Edge as much as possible, but it's expecting new revenue from increased use of Bing, which is tightly integrated with Windows 10. The Cortana-Bing scenarios that Gavin cited -- buying concert tickets, clothes and pizzas -- presumably produce revenue for Microsoft.

Nor was this the first time that Microsoft has emphasized its own properties in Windows 10. When users upgrade from an older version of Windows, for example, Edge is made the default, even if those users had set another browser as preferred in Windows 7 or Windows 8.1.

The timing of the change -- it's unclear why this wasn't established at Windows 10's debut or why, unlike virtually all other changes, it wasn't previewed in the Insider beta builds -- also meshed with Microsoft's strategy of steadily ratcheting up pressure to adopt, and thus use, Windows 10, whether the repeated nag notices to upgrade that appear on older PCs to support limitations on selected hardware.