Sometime back, Mozilla has added about:performance page to Nightly for developers, this page shows how installed add-ons and web pages running in tabs are performing. With the Firefox 47 release, the company has made it available to public. One way users can utilize this page is by disabling system add-ons (Firefox browser doesn’t let you uninstall them), which they no longer use, such as Firefox Hello and Pocket.

Disable Pocket and Hello System add-ons in Firefox release or stable

1. Visit about:performance page, under ‘Performance of add-ons’

Firefox 47 final about performance page

2.  Click ‘Disable‘ button for the system add-on you want to remove. You can always see extensions installed by you in add-ons manager, which doesn’t list Pocket and Hello.

Note: You can still use, customize menu or about:config preference to hide or remove Pocket icon/feature. You can remove Hello or Pocket system add-on by deleting their respective xpi file.

Follow the below link for that

How to remove Firefox Hello System Add-on?