Firefox can save pages in PC. The mobile version should also add a save page button.
When people can save pages, it will allow visit pages when offline, faster page load speed and use lesser mobile data.
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I second this. Especially for PDF I cannot use Firefox at all. I need to revert to another browser to save the actual PDF. Firefox will print the PDF to PDF which makes it useless in some cases.
Have you looked into pocket? You can share websites with pocket to save them there. It's an external app but also run by Morzilla I think. It's also integrated into the desktop version of Firefox to some degree.