Earlier quoted context omitted.
> one has to trust Mozilla not to do that. Exactly. One has to trust Mozilla every time one visits the page . They could easily configure it to be malicious one time out of a million (say); what are the odds that they would be caught? Web-page-based crypto is fundamentally insecure, and Mozilla is committing an extremely grave error in encouraging users to trust it (as they also do with their Firefox Accounts). Secur…
I don’t think the second paragraph is a logical extrapolation of the first. If this is using the WebCrypto API (which it appears to be doing), then trusting this browser-based solution isn’t fundamentally different from trusting an installed application that can update itself.
Using in-web-page crypto gives users a false sense of security. This is, I believe, a very real problem.