This permission is related to credit card autofill, which we enabled in the latest Proton Pass release. 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.

Previous versions didn’t require this permission because they didn’t support credit card autofill across iframes.