If you're referring to the permission to access browser activity during navigation, this is related to credit card autofill. To make this feature work reliably, we need to analyze iframes on web pages.

The only way to do this properly in a browser extension is through the webNavigation frames API. Specifically, we use webNavigation.getFrame and webNavigation.getAllFrames to resolve frame URLs and parse the sub-frame hierarchy during cross-frame autofill sequences. This is exactly what this permission is used for.