Import Word Document results in an unexpected numbered list to appear on the page

Summary

The text in the first row and first column of a copied table will appear outside of the table if you copy paste it while using Firefox.

Steps to Reproduce

1. Navigate to an existing space in Confluence.
2. Click on ... > Import Word Document.
3. Upload this Word file: Numbered heading.docx
4. Click on Import.

Expected Results

The Confluence page should look exactly as it does in the Word document.

Actual Results

There are random numbered lists in the Confluence page.