Could you describe this problem in more detail? For example: * The add-on's toolbar button is no longer displayed * The add-on's drop-down panel no longer fills in, or displays an error (if there is a message, what does it say?) * The add-on's right-click menu item no longer displays * Something else... In case the add-on is not enabled, you can re-enable it on the Add-ons page, Extensions list. More info in this article: [[Disable or remove Add-ons]] (except you'll be clicking the slider switch to re-enable it). If the add-on is enabled but not appearing anywhere, are you using a private windows? Add-ons need permission to run in private windows. See: [[Extensions in Private Browsing]].

See also this article about the Firefox Password Manager. *https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins