Browsers can only protect against malicious websites and malicious extensions. They can't protect against malware. Even without any cert problems, malware on yo

Browsers can only protect against malicious websites and malicious extensions. They can't protect against malware. Even without any cert problems, malware on your machine can modify the browser executable/process to insert whatever code it wants. With this reduced threat model, it's easy to simply keep existing pre-installed extensions available, and disable updates. Your only problem is if a pre-installed extension is malicious or has a vulnerability, it will remain.