http://spywarcbzke2e6skl7wjwtmmnrkslue24cld6kfcufjhhwxtceogmuad.onion/articles/firefox.html
"We may also share your device ID with third parties in connection with advertising campaigns. " And they work with advertisers too! Describing all of Pocket's violations would take up this whole article. There are similar services with better privacy policies, but in the end, they still store the things you view in "the cloud".