The "Take Screenshot" feature and "Save full page" option is useful because pages that render properly on screen cannot usually be printed to a PDF file without some formatting trouble in comparing the layout of the screen and the layout of the PDF saved version.
We have found that using a different browser like Chrome or Edge illustrates with different results, there is something fundamental about Firefox converts to PDF and how other browsers convert or print to PDF.
The problem with the "Take Screenshot - Save full page" feature of Firefox is that the resulting image is tall and narrow and we do not have an easy way to convert the image to PDF for standard size paper fitting to the maximum width of the page.
I think further development in properly converting web pages to accurately rendered PDF files would be welcomed by Firefox users.