Open ADR File
ADR extension files are a type of Bookmarks created by Opera for its Opera Software browser.
More about Opera
Opera is a cross-platform web browser developed by Opera, which bears the same name.
Opera is based on Chromium, however, it is distinctive from other Chromium-based browsers due to its user interface and other features.
ADR files are for configuring and adding features to the browser, specifically for marking visited pages.
ADR files are not designed to be opened manually.