I don't know it it's a bug or a missing feature. If for example I visit a news website, scroll down a few articles and choose to read article 4. The new page will load in the same tab so I can read the article. If I go back, I'm back at the top of the news website, like the first time.
It would be really useful that Firefox saves where I was when scrolling the first page, so that I can continue at article 5.
And sometimes, when visiting a new link and expect to be at the page's start, Firefox shows me anywhere else and I have to scroll back at the top.