Do you have ads every page you go on your Firefox?

[Dynamicaftermath380]

I know it's normal, but recently, even my Facebook, Twitter, and YouTube have ads. What strange is under those ads have the caption: "Ads not by this site"?

So what's up with that?

[A]

I use Ad-block plus, I never see ads.

[DunbarPappy®ϟϟ]

Try "MalwareBytes" to start cleaning up your system:
http://www.malwarebytes.org/

FIREFOX: Tools> Options> Privacy> top drop slot set to "Firefox will use custom settings..."> Check 'Accept Cookies from sites' &
â–ºUn-Check 'Accept 3rd Party cookies'.

A good collection of effective security & privacy add-on's (Official Mozilla) is here:
https://addons.mozilla.org/collections/d...nbarpappy/
â–º"AdBlock Plus" (with 'subscription' added) helps defray rubbish.
â–º At minimum, get the #1 item for malware prevention: "NoScript", which constrains automagically fetching & deployment of potentially tainted assets, and offsets the Microsoft install if it's rubbish.
Bookmark and refer to this page for how it works, and how to use it when sites don't function quite like you need: http://noscript.net/features#contentblocking