For ages I could not work out why google ad's included within a wordpress page didn't work (in fact this applies to a post too). When google support pointed out that there was \<br/> 's in my code the penny finally dropped.
So here's the deal, I pasted the following code into my page: (In the wordpress dashboard)
firefox ad \
adsense ad
Wordpress adds page formatting to the java script that is posted, so if you look at the source, what you actually get is...
\