spdpro, thanks for your input. It helped me figure that the issue was with my installation.
I also have firefox version 53.0.3 with Adblock plus (ABP). I uninstalled and re-installed firefox, which did not help.
But when I tried to report Ad issue to ABP it indicated that I needed to install filters. After I installed filters "Blockzilla" and "Easylist" ads went away.