And neither is the Temporary Containers Addon. I just did fresh brand new initial Firefox install on both the most updated version of Windows 10 and the most recent version of Ubuntu 20.04. All addons appear in the toolbar except these 2. I've tried installing these 2 first. I've tried installing them last, then disabling all the other addons, uninstalling them and reinstalling them. Nothing will make them appear in the toolbar, yet they appear as enabled when they display under the addons > extensions. Also, hitting the extension shortcuts will not bring up the addon interaction screen for any of the addons, e.g. Ctrl U or Ctrl <period> or whatever the relevant shortcut command is. This appears to only be an issue with FRESH Firefox install, because on my other computer running Windows 10 I've had the Multiaccount Containers Addon in the toolbar for 6 months without issue through many older versions of Firefox; and after I updated (rather than fresh install) to this latest version the Multiaccount Containers Addon remains in the toolbar without issue.

Can anyone suggest how I can get theMultiaccount Containers Addon and Temporary Containers Addon to appear in the toolbar? And why are none of the extension shortcuts working - could I be executing them on the wrong screen? I've been trying them on the Addons > Extensions screen.