The WebExtensions API is Firefox’s extension framework. It gives add-ons a standard way to interact with the browser, request permissions, and use features such as tabs, storage, and, when allowed, cookie or site-data access for specific domains. This permission model is powerful: it lets legitimate extensions automate tasks and customize browsing, but it also creates a security boundary that users must trust.
In attacks, a malicious extension can abuse granted permissions to read session cookies, alter web pages, or act on behalf of a logged-in user without knowing the password. That makes the API relevant to account takeover and post-login abuse, where stealing a live session may be more effective than phishing credentials. Defenders should review extension permissions carefully, limit installs to necessary add-ons, watch for suspicious updates, and treat browser extensions as part of the identity and session security surface.