As someone involved in the WebExtensions Community Group who has been (slowly) trying to figure out what, if anything, we should do at the platform level around these use cases, I appreciate you raising and repeating this concern. I'd be obliged if you have any other recommended reading around this topic.
Oh, this is interesting! I assume most of the heavy lifting to identify and filter content is being performed by the content script. In practice have you see any issues with models accessing page content before the extension has been able to sanitize the page?
Do you mean Firefox on iOS? If so, that would require the firefox-ios project to adopt BrowserEngineKit, which is relatively new. Firefox for iOS WebExtension support is being tracked in https://bugzilla.mozilla.org/show_bug.cgi?id=1497374
Just took a quick glance at your extension and observed that it's currently using the "debugger" permission. What features necessitated using this API rather than leveraging content scripts and less invasive WebExtensions APIs?