[Markdown] Firefox folder to markdown prep

[Rumyra]

Tracking issue for the work which needs to be done to convert firefox folder to markdown

• remove id attrs expect on headings
• deal with hidden code blocks in live samples
• remove hidden elements not associated with live samples
• remove summary and seoSummary classes
• remove inline styles
• make note/warning consistent
• fix dls
• deal with sup sub
• remove random css classes
• remove unsupported elements
• ensure tables are converted appropriately
• fix any <strong><code> markup or other inline issues

[Rumyra]

• Check for title as well - there's a few scattered around on anchors