Lines are too long; page width does not scale properly with font size

In my browser (firefox), lines are around 132 characters long. On the previous website we had something like 95 characters which is already a lot.

Also, the page width is expressed in absolute terms it seems. When scaling down the font (with CTRL- in firefox), lines get longer and longer in terms of characters. I think that this is not proper behavior.

Both problems were solved in the old site with the entry

body {
    max-width: 55em;
}

in CSS. Surely this must be also possible with bootstrap?