Thanks for the suggestion! I would love to provide password protection, but Mozilla's recent changes to Firefox have made it practically impossible for an extension to provide behavior like this. Hopefully they will add back this functionality in a future release (but I'm not holding my breath). One solution is to use a FireFox clone like WaterFox, which unlike FireFox still supports older extensions. You can then load another extension in conjunction with FSS, such as ProCon Latte. This offers password protection for add-ons.

Regarding #2, it sounds like the problem is on the YouTube side. If a clip is mistakenly marked as restricted on YouTube, there's no way for this extension to know that. This extension makes no choices about what content is blocked or not - it simply informs the site (e.g. YouTube) that it should enforce the safest viewing/searching settings.