Slider in header creating ultra wide container

I have spent the day trying to create a background slideshow in the header, first using Meteor Slides and now with MetaSlider.

As a result of countless searches, I am now getting there except for one problem which I cannot understand.

Both the slideshow plugins create a very wide container which breaches both left and right boundaries of the header. I have moved the slideshow images to the right which leaves an empty white box on the left with a bullet point in Chrome but not in FireFox. FireBug shows this wide container but I don’t seem to be able to get to it.

I am frustrated beyond belief so any help would be gratefully appreciated.