Is this on all websites or only certain ones? Some websites use "infinite scrolling" which means it is up to the web site itself to return you to the correct point after you use the back button.

Google does not use infinite scrolling, so if you click on a Google search result and then use the back button to return to Google, you should end up at the same position as before if everything is working correctly.

If so, then the issue you are having would be a problem with the other website itself rather than with Firefox.

Thanks for your answer. One site Win10 support works right in Opera but not in Firefox. This seems to happen more in forums.

I have no issue on that site with Firefox, I can use the back button and end up half way down the page where I was before.

Have you tried running Firefox in safe mode to see whether the problem still exists? This temporarily disables all add-ons so it is very useful to work out whether the problem is with an add on or internal to Firefox itself.

Do you mean Windows' safe mode or is there a Firefox safe mode?

This is done via the (disk) cache, so make sure that the cache is working and that you do not use Private Browsing mode. Some websites may instruct the browser not to cache their pages (Tools -> Page Info -> General might show this).

Problem solved! I disabled Saka Key and everything works.