Use the browser.topSites API to access the top sites that are displayed on the new tab page.

Permissions: topSites

Not allowed in: Content scripts, Devtools pages

_GetOptions
MostVisitedURL
_MostVisitedURLType
get
_MostVisitedURLType: "url" | "search"

The entry type, either url for a normal page link, or search for a search shortcut.