At the time of this writing, there is a well known bug in Bootstap CSS, where an undesired horizontal scrollbar apperars on your pages. A long discussion thread about the bug can be found here

The solution that I found to work best is to add the the commant overflow-x: hidden; to the body class of your custom.css file.

1. In the directory where you keep your CSS files, crete a new file called custom.css, if you don't have it already.
2. Add the following code to the file:
   

   body {
       overflow-x: hidden;
   }