FP will create fairly standard HTML code with a few exceptions. Typically
though, it's renderable in pretty much all browsers. The difficulty though
comes in the design choices made. FP will do what you tell it to as will
other WYSIWYG editors. The problem is, what you tell it to do is not always
compatibile with other browsers. For example, you have to use absolute
positioning just right to get it to work in multiple browsers as each
browser has it's own idea of how to interpret the HTML. Some features, such
as Word Art, are not cross-browser. FP turns off a lot of features and greys
them out, but users can turn these features on by changing the target
browser type in the options without realizing the ramifications.
Posting a URL here will let us peak at the code and tell you what could be
causing the problem and what your best step may be to correct it.