The extension wants "access to browsing data", whatever this means.

There are no real benefits compared to just using the website, as it just opens a new tab with the selected text pasted into.

I want to know if the extension could work without that permission, and will just use the website for the time being.

greasy loopholes in the privacy policy

The inability to scan a webpage is a disappointment.

Selecting text can be troublesome. It's sometimes necessary to use the View menu of Firefox to switch from 'Basic Page Style' to 'No Style', after which the context menu for selected text does not have the required effect.