in the file browser/components/newtab/RemoteNewTabUtils.jsm the LinkChecker creates codebase pricipals to check if uri's can be loaded for the new tab page. somehow we need to get the user context id for the tab showing the new tab content. it doesn't look like there's any docshell/document/channel in this file anywhere so we're going to have to use some other means to get the current user context id. we do want to isolate the new tab content based on user context id.
This should be RESOLVE WONTFIX because this file does not exist any more.