In the settings you could set so that sites you bookmark is saved and also link the bookmark to the saved file locally if you want to.
[1] https://addons.mozilla.org/en-US/firefox/addon/single-file/ [2] https://addons.mozilla.org/en-US/firefox/addon/singlefilez/
But if we're looking for a developer side solution, then making pages that last an order of magnitude longer may be better for everyone in the long run, e.g. https://jeffhuang.com/designed_to_last/
I like the ability to use tags too -- I've got various product/tech ideas and it's nice collecting information with it and not having to worry about the pages going away or changing.
Of course I cannot vouch for their respect for privacy.
[0] https://apse.io
web developer menu
toggle tools
select ...
select settings
turn on "take a screenshot of the entire page"
now you get a camera icon. clicking it snapshots the current webpage (as a veeery tall image)
And then when I return, I get a 404. Instead of bookmarking, I'd love to "capture" the current info, divs, and graphics.