The company apparently has a plan, but no timeline

Pocket incorrectly stated in a recent Mozilla support article that the service would not work on Kobo e-readers after Pocket accounts were moved to Firefox. Pockets integration is an important offering Kobo provides to e-reader users and we will continue to maintain our support through the Firefox transition. The Mozilla team has updated that article to now include the relevant information.

Kobo users logged into an existing Pocket account will not be affected. For new Pocket users with accounts created after August 15, the e-reader update will be required and Kobo will have a new sign-in flow to support Firefox accounts. Existing users who wish to switch to a Firefox Account to login will need to update their e-reader at that time to continue using Pocket.