I, an autist, am used to the old version of bookmarks where the new ones go at the bottom. This is very handy, as it thereby ranks my bookmarks in chronological order, oldest at the top. This is perfect for me, as an avid albeit somewhat disorganised reader with several hundred loose and uncategorised bookmarks. I have a system, okay?
Currently, new ones go at the top. This has completely destroyed my user experience, to the point that I am seriously considering switching to another browser.
I like Firefox, so I thought that maybe... changing to ascending or descending being an option you can change client side would be best. As many appreciate either ascending or descending bookmarks for different reasons.