Firefox lets you know when addon changes permission between versions. You are prompted to accept the new permissions before upgrading the addon. This has been helpful in weeding out addons that become too data hungry.
So once they are ready to add malicious code in the future to pass that information somewhere else, no permission changes will be required.
Before downloading any extensions, I usually inspect them quickly with https://chrome.google.com/webstore/detail/chrome-extension-s...
Most important parts are "manifest.json" and then if defined then content scripts that match catch all urls and "https://*/*" / "http://*/*.