I have a set of bookmarks that fit the page in the window. I added a new bookmark when I was zoomed in to part of a page. That's what I wanted for my new bookmark. However, all the other pre-existing bookmarks also changed their zoom level when the new bookmark was added. How can I make already created bookmarks keep their original zoom level when a new bookmark is added?
Creating a new bookmark does not (or at least should not) change the zoom setting associated with other bookmarks.
However, if those bookmarks are set to Inherit Zoom then once you're zoomed in (as a result of pressing that new bookmark, for example), that zoom level will be maintained when you click them. You'll need to change it to something else if you don't want that to happen.