Extension signing is a browser security control that requires add-ons to carry a valid digital signature before they can be installed in a release build. The signature proves that the extension was approved for distribution by the browser vendor or another trusted signing authority, and it helps the browser reject tampered or unsigned packages.
This matters because browser extensions often run with broad access to pages, storage, and user inputs. In attacks, signing does not stop a malicious developer from publishing a deceptive but properly signed add-on, nor does it protect users who install from the wrong source or disable safety checks. In defenses, signing helps block random malware, supply-chain tampering, and modified extension files, making it harder to load untrusted code into the browser. For security teams, it is one layer of trust verification, not a guarantee of legitimacy.