When storing cookies is disallowed, the extension can not edit and read the channel list anymore. There are two ways to fix this: either generally enable cookies or explicitly allow the extension to store cookies. See the following two sections for instructions.
Generally enabling cookies
Go to the browser preferences, select the Privacy & Security section and ensure the History settings either are on Remember history or Use custom settings for history and Accept cookies from websites is checked.
Explicitly allowing the extension
Go to the browser preferences, select the Privacy & Security section and select Use custom settings for history for the History settings. Nothing has to be checked. Click the Exceptions…, open the channel manager in a new tab and copy the URL up until /manager/index.html. Paste the moz-extension:// URI into the Address of website field and click on the Allow button, to permanently let the extension store and access information in the database.