display block doesn't compute images floating

hi there i have this code

<style> 
.sample{display:block;width:100%;} 
.sample img{float:left;} 
</style> 
 
<p class="sample"> 
<img> 
cool text 
</p> 
<p class="sample"> 
<img> 
no so cool text 
</p>

The idea is to display the text with the image at the left (or right, whatever)
this works on IE but not in Gecko based browser. The lasts ones doesn't compute the image for the block. And so start to display wrong or not how i will like to.

Any idea or explanation

Thanks

PD: I also tried using the align of the image Tag.