Odd <div> issue when inserting link.

My code when i load the page:

<div>Boo bop doo dey boo bop</div>

My code when i add a link to a word:

<div>Boo bop </div><a href="http://testing.com" class="brownText">doo</a><div>dey boo bop</div>

Notice how the link is between two divs? No idea why it does that, to be honest. I use <div> instead of <p> cause i don't like the gap above and below paragraph tags and the editor is nicer using divs because the linebreaks aren't so 'gappy'.

I wish i knew why it did this...
Any thoughts?

EDIT: Doesn't affect IE7, only Firefox3.