Annoying pop up ads now claim to be from Firefox and full system scan didn't help me.

Question

Pop ups have been appearing in lower left and lower right corners of my screen for many months. I installed Adblock Plus a few weeks ago and they seemed to go away. Now, they have come back. The last ad I clicked on opened a new tab, blank and the spinner was going for a few seconds, I sensed trouble and closed the tab.
While researching on the Mozilla site - I got another lower right ad (purporting to be from Firefox). Hovered the mouse over it and it appeared to show a Mozilla URL in the lower left status bar, but I wasn't about to click on it. The ad looks phoney. I have a screen capture and would love to send it to you. I've got tonight's screen capture (with mouse hover) saved as a JPG and PNG files. Tell me how to upload and I will.
Related or not related to the pop up issue (I'm note sure) is this: Again while researching on the Mozilla site tonight - I did a Control-Clicked on a link to read one of your malware topics and instead the new tab opened to a site called local.com. For a long time (a year) I have had the problem of being taken off to some unwanted web sites when using Control-Clicks. Angy.
In all these months, Windows Security Essentials is always on. I've run several full scans. Never find things. Do my best to keep all software and virus info up to date. Damn pop ups just keep happening. I can't tell you if these things happen with Windows Explorer cuz I don't use it much.
Would like to scream - if I knew it would help. Tell me what to do next. Thanks.

Answer 1

Install, update, and run these programs in this order. They are listed in order of efficacy.<br />'''''(Not all programs detect the same Malware, so you may need to run them all to solve your problem.)''''' <br />These programs are all free for personal use, but some have limited functionality in the "free mode" - but those are features you really don't need to find and remove the problem that you have.<br />
''Note: If your Malware infection is bad enough and you are mis-directed to URL's other than what is posted, you may have to use a different PC to download these programs and use a USB stick to transfer them to the afflicted PC.''
Malwarebytes' Anti-Malware - [http://www.malwarebytes.org/mbam.php] <br />
SuperAntispyware - [http://www.superantispyware.com/] <br />
AdAware - [http://www.lavasoftusa.com/software/adaware/] <br />
Spybot Search & Destroy - [http://www.safer-networking.org/en/index.html] <br />
Windows Defender: Home Page - [http://windows.microsoft.com/en-US/windows7/products/features/windows-defender]<br />
Also, if you have a search engine re-direct problem, see this:<br />
http://deletemalware.blogspot.com/2010/02/remove-google-redirect-virus.html
If these don't find it or can't clear it, post in one of these forums for specialized malware removal help: <br />
[http://www.spywarewarrior.com/index.php] <br />
[http://forum.aumha.org/] <br />
[http://www.spywareinfoforum.com/] <br />
[http://bleepingcomputer.com]