Addons are not allowed to inject content scripts on addons.mozilla.org. Per https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Content_scripts, injecting a content script on AMO, causes a CSP error to be logged. This is AMO policy, and no web extension which relies on a content script will work on AMO.

Regarding the settings not being saved, I cannot reproduce this, so can you provide step by step instructions? Please note that once a setting is changed, you might have to reload already loaded pages for the settings change to come into effect.