Not sure if anyone noticed, but when viewing Montezuma on a narrow viewport, you can scroll to the right by 30 pixels, right past the edge of the site:

And if you do so, you can see nothing but unused blank space along the side:

Naturally, I was puzzled by this. So today I spent some time digging around to find out what the cause for this is, and how to fix it.

Turns out there is a 30 px left padding applied to the breadcrumbs and, unlike any other elements in Montezuma, breadcrumbs box is not being treated with the box-sizing: border-box; style. So any padding gets added to the existing size of the box:

The Fix
The solution is to place the following code to the top of Montezuma Options > CS Files > clearfix.css:

/* Fixes the horizontal-scrollbar-white-space issue created by breadcrumbs padding */
#breadcrumbs1 {box-sizing: border-box;}

Presto!

EDIT:
It's curious that this bug exists, especially since Montezuma already applies this fix to every HTML element via wildcard:

I've noticed that before. What's even more curious, though, is that right after the rule which sets all of the elements to box-sizing is this rule:

.row, .lw { 
	-moz-box-sizing: 		content-box; 
	-webkit-box-sizing: 		content-box; 
	box-sizing: 			content-box;	
	o-box-sizing: 			content-box;
}

Don't know the reason for this rule, but what I've done is copy this rule to my various.css file and change content-box to border-box. This takes care of the breadcrumbs bar since it has a class of lw assigned to it, which is why border-box wasn't being applied to it. This fix doesn't seem to negatively impact anything else that I can tell.

I think the real cause it that once the screen gets smallre thann 767, the meny flips to the the pull down and there is a 30px left margin on the breadcrumb

#breadcrumbs1 {
	padding: 				5px 0 5px 30px;
}

try adding this code in breadcrumbs.css so you end up with

#breadcrumbs1 {
	padding: 				5px 0 5px 30px;
}
@media only screen and (max-width: 767px) {
  #breadcrumbs1 {
	padding: 				5px 0 5px 0px;
  }
}

Thx JD, I actually like the 30px padding. I'll use the solution I posted in the original post, I like your idea of appending it to breadcrumbs.css instead of clearfix.