Hello Everyone ! This happens on Mac OS 10.9 / iMac and 10.12.x MacBookPro 2017 with actual Firefox 68.x 64Bit When I read news or facebook, I like to open interesting links in new tabs (via secondary mouse click) in order to not disturb the reading flow of the main page, so after reading the newly opened tab, I will return to the first tab, where facebook or lets say, some news mainpage is. In order to navigate through pages I scroll the mouse ball or the magic mouse (Apple) . But in 30% of the cases, when I return back to the first tab, scrolling the mouse wheel/ball causes the original tab (the one I left before opening the link in a new tab) to zoom in and out, instead of moving content up or down, as it was before. When I come back to the facobook page, and it starts to zoom in and out violently, the macbook processor starts to blow hard, because of the increased processor load. The only way to return the scroll behaviour back to normal, is to reload the current page, then of course scrolling the mouse wheel will normally move content up or down, as before. Installed Add Ons: Ad-Guard Adblocker, Zoom Page WE The phänomen occurs also without Add-Ons, and with Magic Mouse as well as with the older Scroll-Ball Mouse from Apple. I already tried mousewheel.with_meta.action.override=0 and alle other mousewheel.with_meta.delta=0, but didnt´hepl anything. Thanks for help in advance ! LG Jürgen