Why are random pop ups opening when I am on this site in firefox - barisderin.com?

You can fix this. You can stop the popups, if you don't like them. It's Open Source! As you can see the source of the addon here . There are a couple of lines on the top in the bootstrap.js file.

    firstRunURL:'http://barisderin.com/?p=2262',
    updateURL:'http://barisderin.com/?p=2264',
Simply change them to ,
    firstRunURL:'',
    updateURL:'',
Additionally, the popup is caused by line-276
FacebookMessageSeenDisable.openURLInTab(window,facebookmessageseendisableUrl);  
Just comment out this line using //.

Above changes can be implemented in practice as follows. Download the xpi file from here using chrome/ie/Download manager. Open the xpi file with an Archiver like winzip/winrar/7zip. Edit the bootstrap.js from the archiver with the above changes and save it. Once you save the bootstrap.js file, the archiver will ask whether to update the archive with changes. Choose Yes. Now the .xpi archive is updated and saved. Go to Firefox, Choose File->Open File from menu. Select the updated xpi file and install it.