'do not track' doesn't prevent a webpage from connecting to advertising websites. 'do not track' may lessen the amount of advertising you see, but it doesn't block it 100%. Are you using an "ad blocking" extension, like Adblock Plus or uBlock Origin? Those would be more effective at "ad blocking" than 'do not track', which is a voluntary compliance feature; websites don't have to honor that setting. Even the "ad blocking" extensions allow "less intrusive" advertising; the user needs to select "strict compliance" {uBlock Origin} or "block unobtrusive advertisements" manually {Adblock Plus} - neither blocks all ads automatically or upon installation.

That said about "ad blocking" - many popular web sites are blocking users from using their website when they detect the use of an "ad blocker". So there is no way to 100% block all advertisements

Start Firefox in Safe Mode to check if one of the extensions (Firefox menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes