Firefox Redirects Random Websites?

My problem is that I use Firefox (main browser Win 7) to browse and every so often it will redirect my websites to adware. For example when I "middle click" on a site at Google or Reddit, it usually opens a new tab but sometimes it opens this completely other site which im guessing is malware, I use Adblock Plus so not every malware site redirects to it, a lot of the time it is just a blank page with an obvisouly incorrect URL. I used to be able to browse just fine, but now it seems every so often that it wants to redirect me to this other site. MSE always pops up telling me it wants to send a ".tmp" file to Microsoft because it doesn't know what it is. But whenever I use MSE or Malware Bytes (even on the full trial version, or rootkit scan) it never picks up anything when it has been scanned. I have scanned it normally and on Windows safe mode.