Not sure if you tried that. Chrome has a take full page screenshot command. Just open the command bar in dev tools and search for "full" and you will fund it. Firefox has it right in the context menu, no need for dev tools.
Unfortunately there are sites where it does not work.
Apart from small UX nits, FF's screenshot feature is great - it's just that storing a 2-15MiB bitmap copy of a text medium still feels dirty to me every time.. would much prefer a PDF export, page size matching the scroll port, with embedded fonts and vectors and without print CSS..