I'm not putting words in your mouth, you literally said this is a "Good Thing (tm)", because of hypothetical security reasons. Whereas I'm literally saying that this actually broke real privacy extensions, broke peoples software, and badly damaged their reputation.
As to your argument about security: doing the check on install instead of all the time, as I suggest is preferable, still protects against MITM and malware. The only argument for expiring software based on a calendar is that it might be a security risk if it's out of date. But first off, that is highly dependent on what the extension actually does. Also clearly we can see it's also a security risk to turn off privacy extensions without warning based on an arbitrary signing certificate.
Things might change after install. Its a Good Thing (tm) to periodically recheck, or check revocations.
> > I'm not putting words in your mouth [..]
Yes, you did:
> "So you think [..]"
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Instead of disabling this historically working feature which normally works great against hostile attacks such as MITM and malware this problem would've been avoided by a simple cron script which runs daily, and checks for expired certificates used within the infrastructure (both interaly used and externally used).
The main competitor you mention, Google Chrome, is a terrible privacy hazard. This situation does not change that.