It's a malware distribution campaign that strikes in waves, moving through ad networks on popular sites. Good instinct to avoid it. You may want to consider using an ad blocking extension -- you can make exceptions for sites that you want to support. Here's a popular one:

https://addons.mozilla.org/firefox/addon/ublock-origin/

I'm getting this a lot, too. It happens quite often on yahoo.com, but also other sites. Did you install this ublock that was suggested? It says it has to have permission to "Access your data for all websites" and other things that sound troubling. Thanks