I stick to extensions that Mozilla has manually vetted as part of the Firefox recommended extensions program.
> Firefox is committed to helping protect you against third-party software that may inadvertently compromise your data – or worse – breach your privacy with malicious intent. Before an extension receives Recommended status, it undergoes rigorous technical review by staff security experts.
> Firefox is committed to helping protect you against third-party software that may inadvertently compromise your data – or worse – breach your privacy with malicious intent. Before an extension receives Recommended status, it undergoes rigorous technical review by staff security experts.
https://support.mozilla.org/en-US/kb/recommended-extensions-...
I know that Google hates to pay human beings, but this is an area that needs human eyes on code, not just automated scans.