Firefox VDH hangs when verifying companion app?

[Simon Lambourn]

Using Firefox on Ubuntu 22.04 (not snap - removed snap & installed 102.0-1 64 bit from ppa to get round snap problem with coapp).

VDH settings page says "verifying companion app...", and when the Recheck button is pressed, it never returns.

Firefox browser console shows an error when the settings page is opened:

Error: Please use $(ref:runtime.getURL). main.js:1
    open moz-extension://c0daeaee-5636-46a7-a099-9eb52efd19b1/background/main.js:1

(excuse formatting - see attached screenshot)

And a further warning & error when the Recheck button is pressed:

(Warning) LoginRecipes: getRecipes: falling back to a synchronous message for: moz-extension://c0daeaee-5636-46a7-a099-9eb52efd19b1 LoginRecipes.jsm:297:11

(Error) ExtensionError: Attempt to postMessage on disconnected port ExtensionUtils.jsm:58:5

    ExtensionError resource://gre/modules/ExtensionUtils.jsm:58

    send resource://gre/modules/NativeMessaging.jsm:243

    onPortMessage resource://gre/modules/NativeMessaging.jsm:131

    recvPortMessage resource://gre/modules/ExtensionParent.jsm:378

    recvPortMessage self-hosted:1115

    _recv resource://gre/modules/ConduitsChild.jsm:82

    receiveMessage resource://gre/modules/ConduitsParent.jsm:450

VDH version 7.6.0, co-app package net.downloadhelper.coapp-1.6.3-1_amd64.deb

Is this a bug or is there a firefox/VDH setting I can change to solve this?

Thanks for your help.