You click a link, sign in, approve the MFA prompt, and get on with your day. Completely unaware that someone else just logged into your account at the same moment.

That scenario surprises many businesses, particularly those that rely on multi-factor authentication (MFA) to protect cloud accounts.

MFA is a strong front-door lock. But it’s not the only thing that decides whether someone can get in.

After you sign in, your browser keeps you logged in using a session token (often stored as a cookie). It’s the digital version of a wristband at an event: once you’ve been checked, the wristband proves you belong there.

Browser add-ons have a funny reputation. They feel “small”. A quick install. A tiny productivity boost. A harmless little helper that lives in your toolbar.

But in practice, a browser extension is more like a micro-SaaS vendor sitting inside your browser session.