I've been using this a few days. So far it seems like a very good browser add-on overall, it does what it says it will do. I have a few suggestions to improve it:

1.) It says: "users cannot override the safe search settings enforced by this plug-in." but that's not quite true. It should be password protected so it is not easy for anyone to go into Add-ons Manager and simply click "Disable" to disable the Force Safe Search . For example, a typical reason someone might use this is to configure their child's computer to force the Safe Search mode ... if it's disabled with a single click in the Add-Ons Manager , even a child can figure that out easily.

2.) Allow some exceptions that the user can set up in a preference panel. For example : on YouTube , if I click on a video that has been flagged as "Restricted" it tells me I can't view it unless I sign in with my Google Acct. and turn off "Restricted Mode" ... but if I do that it still won't let me see the video . (it overrides my turning off Restricted Mode ) . And what I'm talking about is not really 'questionable' content , the clip I first noticed this behavior on was a clip from the Coen Brother's film 'Inside Llewyn Davis ' https://www.youtube.com/watch?v=9Aq4a7g_wdU . No idea why someone has flagged this harmless clip as "Restricted" . But it wasn't even the result of a search , it was just a clip that a friend posted on YouTube , I clicked on it to watch, couldn't watch it until I disabled "Force Safe Search " . So I think it could use some tweaking in terms of what it is blacklisting automatically.