Are you clearing your recent history when you close Firefox?

Firefox stores App Tabs and tab group details in the same file that stores details of browsing sessions. Make sure that you have not set Firefox to delete browsing history. For details of the setting to check see https://support.mozilla.com/kb/Clear+Recent+History

Thanks Tony. That did it.

So it looks like I need to give up the feature to clear history (or use CCleaner) if I want to use the App Tab feature. Is there any way I can have BOTH?

It seems it would be nice, in the Clear History dialogs, if the App Tabs could be excepted.

Thanks again.

I should not have to save browsing history to save App Tabs... App Tabs are great, but not at the expense of the browsing history. Bad design decision imho.