Phony New Tabs keep popping up

[Newmaven]

My default browser is Firefox, but I often use the SeaMonkey browser.

Clicking on many sites in SeaMonkey makes Firefox open too, to new tabs with addresses such as syndicate.twitter.com, https://rd.about.com/boomerang, and ae810539.mpstat.us.

What are these, and why do they pop up?

 

[Newmaven]

Here's another:

http://analytics.youramigo.com/owa/log.php.

This one doesn't just say new tab but "log.php (GIF Image, 1 x 1..."

 

[alphaniner]

That last one seems like it could be a tracking pixel, and at least a few of the others seem tracking related too. I don't know much about SeaMonkey, but there's the common FF troubleshooting questions: Do you use any addons? Does the behaviour occur with a fresh profile?