Strange Bug Rated 4 out of 5 stars

A very good and useful addon. But I noticed a strange bug.
When this addon is activated, and a new tab is opened in the background (right click on a link - open in a background), the page scrolls down by itself, it scrolls down about 50 pixels.
But this only happens when the page was already scrolled down. It starts happening when a page was scrolled down about 30-50 pixels.
If you need any additional information, I'll gladly provide it.

System: OS X Mavericks, Mac Book Pro.