I work with many tabs open and i use the mouse scroll wheel to scroll thru them, since forever the scroll wheel behaved the same, you scroll up (push the scroll away from you) and it scroll to the end (right) side of the tabs, you scroll down ( pull the scroll wheel towards you) if scroll to the start of the tab bar (left). today to my surprise i opened firefox and immediately noticed this change... no extensions were installed or uninstalled nothing was changed since last use.