Pasting formatted content into code block loses code structure

Phenomenon

When pasting formatted content (with HTML formatting) into a code block in Firefox, the formatting is preserved but the code block structure may be lost. The code block may be converted to regular paragraphs.

Reproduction example

1. Create a code block: <pre><code>function test() {</code></pre>
2. Paste formatted HTML content into it
3. Observe the DOM structure

Observed behavior

• Code block structure is lost
• <pre><code> may be converted to <p> elements
• Formatting is preserved but code context is lost
• Code block is broken

Expected behavior

• Code block structure should be maintained
• Formatting should be stripped (code should be plain text)
• Code block should remain as <pre><code>
• Structure should be preserved

Browser Comparison

• Chrome/Edge: May preserve or break structure
• Firefox: More likely to break structure (this case)
• Safari: Most likely to break structure

Notes and possible direction for workarounds

• Intercept paste in code blocks
• Strip all formatting from pasted content
• Preserve code block structure
• Convert HTML to plain text