My Firefox has a hidden ad-on or hijack that's popping advertisements into separate tabs whenever I interact with some forms or links on benign websites (common websites like CNN, Homedepot.com). This doesn't happen when I load Firefox in Safe Mode, but I need some extensions for work, so this isn't a long-term solution.
I checked my extensions and ad-ons and they are all from trusted organizations.
I've run Malwarebytes, Ad-Aware, HitmanPro, JRT, but they've not been able to remove whatever's causing this. I made sure these programs had the latest updates before running and that my regular anti-malware (Symantec Endpoint Protection) was disabled at the time.
I've cleared all Firefox caches and deleted all cookies, but the problem still occurs.
This isn't happening with IE or Chrome on the same machine, only Firefox. I've tested all 3 browsers with the same forms on the same pages, and only Firefox produces the new tabs.
I checked my recently installed programs and they're all benign as well - there's nothing I cannot account for.
I uninstalled Firefox, rebooted, then re-installed Firefox, but the issue is still there.
Windows: 7 Professional SP1 (64-bit)