Heh, okay, yet another reason to not move from Google Chrome... In an attempt to stay afloat, Mozilla has decided ona move that might be good for it but creates a bad precedens for all of us - namely, it now allows advertisements to show in Firefox' home window, as shown in the screenshot above. Ads will be shown on every platform, from Windows to macOS to Linux.
Interestingly, the ads still do not appear on everyone's browsers. Mozilla might still be testing this feature.