How to avoid horizontal scrolling for all documents in my Mozilla?

Hello everybody. I'm trying to write a component that will be "format" html
content. I would like to avoid a horizontal scrolling
in documents that will be rendered by my Mozilla. So documents will be
rendered not with the native horizontal size but with my
size as good as possible. Does anybody know some easy ways to do that (for
example, maybe Mozilla has
some internal constants that limit the horizontal size of all documents).

Thank you in advance,
Michael