Firefox in embedded mode does not work in the application.
The Firefox web browser is deprecated in embedded mode.
Remote Desktop Manager starts Firefox in a separate application (Embedded32.exe) and then re-parents the application inside Remote Desktop Manager
Firefox does not work when the Team Viewer QuickConnect button is present in the title bar.
To resolve this issue, you need to disable the QuickConnect button in Team Viewer by unchecking the option in Extra – Options – Advanced – Show advanced options – QuickConnect button – Configure – Show QuickConnect button.