Extension permissions are the browser-granted rights that define what an add-on can read, modify, or control. They can cover access to specific websites, tabs, cookies, downloads, clipboard data, browsing history, or browser settings. Permissions are usually requested during installation or after an update, and the browser uses them as a trust boundary around the extension’s capabilities.
They matter because browser extensions run inside a highly sensitive session, often alongside email, cloud apps, and internal tools. If an extension has broad permissions, a compromise, malicious update, or overly permissive design can expose data or alter page content across many sites. Attackers may abuse excessive permissions to steal credentials, inject content, or monitor activity. Defenders reduce this risk by reviewing requested permissions, limiting add-ons to least privilege, removing unused extensions, and preferring models that block hidden code and narrow access.