Comment 3 for bug 1930912

> You want to clear the viewer's search history, right click on the search field and choose "Clear search history"

I did, at step 5.

> The viewer and calibre are independent.

I think there is a dependency: The tooltip of calibre's "Preferences -> Searching -> Clear search histories" button (step 7) says: "Clear search histories from all over calibre. Including the book list, E-book viewer, fetch news dialog, etc.". And clicking on that button clears, among other things, the viewer's search history. It just stays in viewer-webengine.json.