I don't like it when I go back to a tab and it reloads.
For whatever reason, I want tabs to stop changing.
I don't want the to reload from their javascript
and I don't want the tab content to be deleted by the automatic discard (to save memory)
If firefox decides to free memory, it should dump tab data and tab state to disk, not delete and reload from the website later.
Sometimes the website won't exist later.
Somewhat related but this one is hard : Some website dynamically delete content after you've scroll past it (firefox) this means even if you scroll to the "true" bottom, you can't ctrl+f search and you can't freeze the page and read it all at your leisure and preserve it for later.
Currently my solution is to video screen capture the whole tab while scrolling slowly, this is quite a ridiculous step to take but apparently the only option to keep our data !?
While it might be reasonable to expect a web page to behave the way you describe, for anything more in web application territory the expectation that everything you ever loaded will stay visible somehow and available without cooperation of the code implementing the website is ridiculous.
Browser in a VM and a smart enough caching proxy should do.
Especially the narrow case of scrolling up and down the page. That could be scrolling down and disable the erasing of the data, then freezing scripting when it's all in the scroll buffer.