hello, please directly contact the extension developers through the means they make available - they can likely give you more detailed guidance and are the only ones who can fix bugs or make necessary adjustments in the addon for new firefox versions. thank you...

According to PasswordBox, their product is not sanctioned to work with 'beta' versions of browsers so I need to roll back to a non-beta version of FireFox.

Is it simply a matter of uninstalling FF and reinstalling the last non-beta release?

hi lnp00, yes you can uninstall beta and reinstall a regular firefox release version from https://www.mozilla.org/en-US/firefox/all - all your data like passwords, bookmarks and customizations will remain in place...

Thanks Philipp, that did the trick!