The body text is contained in a <pre> tag with newlines for paragraphs instead of the correct <p> tags. You can force Firefox to respect your font choice by add

The body text is contained in a <pre> tag with newlines for paragraphs instead of the correct <p> tags. You can force Firefox to respect your font choice by adding a font:inherit to the <pre>'s css with the developer tools. This will break pages with correctly used <pre> tags.