A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hello James G McLean,
Thank you for providing such detailed information. It helps a lot in understanding the situation. Based on your response, it seems that the issue with the numbering in SharePoint Online text web part occurs specifically when using Firefox. Since the issue does not happen in other browsers like Safari, Edge, or Chrome, we can conclude that it might be a browser-specific issue related to Firefox.
In this case, we strongly recommend that you contact your Microsoft 365 administrator and follow the Online support article to create a support ticket. The support team has higher permissions than ours and can help you check the situation remotely on your end, involve more resources to collect logs, and help you troubleshoot issues. This would be a more efficient way for you to handle this case.
For reference: How do I find my Microsoft 365 administrator? - Microsoft Support?
Best regards,
Sophia