A WebExtension is the standard add-on framework used by Firefox and other modern browsers. It gives extensions access to browser APIs for tabs, pages, storage, menus, messaging, and other features through a controlled interface. For legitimate developers, this makes cross-browser add-ons easier to build and safer to maintain than older extension models.
In cyber security, WebExtensions matter because they run inside a powerful trust boundary: they can read or modify what a user sees in the browser, and they may handle sensitive data before it is stored or encrypted. Attackers abuse this by publishing lookalike extensions that harvest passwords, wallet keys, or session data directly from the extension runtime. Defenders rely on browser controls such as code review, signing, permission limits, and store vetting, but users still need to verify the publisher and install only from trusted sources.