The JabRef Browser Extension “is no longer available because it doesn’t follow best practices for Chrome extensions.” See https://chromewebstore.google.com/detail/jabref-browser-extension/bifehkofibaamoeaopjglfkddgkijdlh.
Thanks for the report! There is an issue for this No longer supported by chrome · Issue #616 · JabRef/JabRef-Browser-Extension · GitHub