Thank you, Yaroslav. You shouldn't worry about the permissions. I've looked into it, but to my knowledge there's no way that I can avoid requesting "access your data for all web sites" if I want to offer users a 'grid of icons' feature. Concerning passwords, an extension cannot access passwords stored in your browser, but the general rule is to only install extensions who's authors you trust. (https://support.mozilla.org/en-US/questions/1225776) This is easier said than done, but if an extension has a good history, the chances you'll get into trouble are reduced. I would personally recommend that, when visiting finance related web sites either use a different secured Firefox profile or visit the web site in private mode. (https://support.mozilla.org/en-US/kb/extensions-private-browsing)