You can save current position in displayed webpage using shortcuts Shift-Alt-0‥9; later, you may return to saved position by pressing Alt -0‥9. Markers created in this way are kept in browser's persistent memory and they will be restored next time you open the page.
Before jumping to marker the script stores the current page position, so you can get back by pressing Alt-minus (that on the right of zero.)
When you open webpage the script tries to restore previously saved position #0.
Positions are calculated in screen's pixels, so if you alter zoom factor, or text column width, or something else, markers may become invalid
press Alt-Shift-0 twice to set starting Y-position for any page in the whole domain
click on pop-up message at top-right corner to remove all markers for current webpage.
You can change script's keyboard shortcuts using GreaseMonkey menu: