This problem is evident in Firefox and not Internet Explorer (there's a first for everything )

Two sets of code:

1.
HTML Code:
<strong>strong text</strong> <em>emphasised text</em> normal text
Note the spaces between the separate parts.

2.
HTML Code:
<fieldset><strong>strong text</strong> <em>emphasised text</em> normal text</fieldset>

The Problem
In FireFox, when the text is in a fieldset, the spaces between the different parts don't show. I don't know whether this is a feature of CSS or not, but I hope it isn't .

Does anyone know why this happens? fixes?