That seems.... odd. I am on Firefox on Windows and I print to PDF all the time using the Windows built-in PDF printer ("Microsoft Print to PDF"), without issue.

That seems.... odd. I am on Firefox on Windows and I print to PDF all the time using the Windows built-in PDF printer ("Microsoft Print to PDF"), without issue. In fact sometimes that printer is the only one that can get things to format correctly! Something on your system might be interfering with the printing process.