What are on these unwanted pages, ads?

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Adblock Plus {web link} Blocks annoying video ads on YouTube, Facebook ads, banners and much more. Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).

Adblock Plus Pop-up Addon {web link} Adblock Plus Pop-up Addon extends the blocking functionality of Adblock Plus to those annoying pop-up windows that open on mouse clicks and other user actions.

Forum; Adblock Plus Homepage {web link}

The unwanted pages are ads and well basically Porn sites which I don't want on my browser, this afternoon I have been running Malware bytes to try and fix the problem , which it is still running currently. I don't want to use ad-block because it defeats the purpose of ads on YouTube but I want to fix the problem, so I may look into it and my Firefox browsers was not opening when I went to look at your reply so I'm currently on Internet Explore is that because I'm running Malware bytes or is it to do with malware its self because I've never had this problem before.

AdBlock can be adjusted to allow what you want, and still block pop-ups.

Malware bytes just finish and it found 600+ malware threats so I hope fixed the issue without needing add block but if the problem continues I may need to look into it thanks for the help

FredMcD said

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.