Both Pocket and Firefox Hello are system add-ons now. Mozilla has done it! It had moved two of Firefox rarely used features as built-in add-ons: first Firefox Hello has been made as system add-on, now Pocket. Latest Firefox 46 Nightly has this change, you’ll notice this when you see the extensions list in troubleshooting information or about:support page. 
You’ll find Pocket XPI file at this location along with Hello’s (as loop): C:Program FilesNightlybrowserfeatures.
Read: How to remove Firefox Hello System Add-on?
Pocket popular known as Read it later, initially available for Firefox as an add-on, Mozilla has integrated this proprietary service into the Firefox browser with version 38.0.5, which annoyed a few users, hope this move will make them happy.
This change –ship features as system add-ons — is a part of Mozilla’s Go Faster project for Firefox browser, “The end goal (of this) is to reduce the time it takes to deliver value to the user. This focuses on getting features and fixes to the user on a reduced cycle time, but includes reductions in time to download updates and new versions, and reductions in build and release time.”
