It&#x27;s difficult for Firefox to determine this.  In this MITM case, Eve is your employer and she&#x27;s modified the cert store that Firefox implicitly trusts.<p>Now it would be interesting if firefox could distinguish between the cert store that it came with and new certs installed.<p>Another idea would be for users to write an extension that could say &quot;such-and-such cert is my employers and you should create a UI flag when it&#x27;s being used.&quot;  I know I looked into that for Chrome and it&#x27;s impossible since it&#x27;s not available to the extension system.