You can check this support article.

• https://support.mozilla.org/en-US/kb/permission-request-messages-firefox-extensions

Content blocking extensions need this permission to be able to inspect what content is requested and possibly block content if items are on a block list. Such extensions usually only inspect the request URL, but in theory extension can go deeper. It is up to you to decide whether to install the extension.

Thanks for your reply, but it essentially just repeats information on your web site. So I will rephrase my question. If I permit an extension to "access your data for all web sites," then can it: (1) see all passwords that I use on any web sites? (2) see all information for web sites in different containers,where I don't use the extension? (3) see information for web sites that I access using a different browser (such as konqueror), but still as the same user? (4) see information for web sites that I access as a different user, on the same computer? I thank you for your work.

1) No, this permission is about content and DOM modifications. 2) Yes, you can't separate it. You use this extension in every container. 3) No, it's only about opened tabs in this browser. 4) No.

Thank you TyDraniu, that is the information I seek. It does seem like an agent wanting to monitor individuals' web use would create a useful extension; evidently there's no practical way to avoid this while using Firefox.