Pasting tables loses structure and formatting

Phenomenon

When pasting table content (from Excel, Google Sheets, or HTML tables) into a contenteditable region in Firefox, the table structure is lost. The content may be pasted as plain text or lose its formatting.

Reproduction example

1. Copy a table from Excel or Google Sheets.
2. Create a contenteditable div.
3. Paste the table content (Ctrl+V).
4. Observe the structure of the pasted content.

Observed behavior

• In Firefox on Windows, table structure is not preserved.
• Table cells may be converted to plain text or lose their relationships.
• Formatting (borders, colors, alignment) is lost.

Expected behavior

• Tables should be pasted with their structure intact (<table>, <tr>, <td> elements).
• Formatting should be preserved where possible.
• Or, there should be a way to control how tables are pasted.