CSS problem Firefox

[xoggoth]

Got a simple drop down from the net that works great in all Browsers except F* Firefox which puts the list further down as though there is an empty first line.

#drop {text-align:left;}
#drop li {list-style:none; float:left;}
#drop li a {display:block; text-decoration:none;}
#drop li ul {display:none; width:10em;}
#drop li ul li {background-image:url('images/dropdown.gif'); background-repeat:no-repeat;}
#drop li:hover ul, #drop li.hover ul {display:block; position:absolute; margin:0; padding:0;}
#drop li:hover li, #drop li.hover li {float:none;}

...etc
...etc

<ul id="drop"><li>Shop</a><ul><li>Crap</li><li>Stuff</li><li>More Stuff</li><li>Things</li></ul></ul>

There's nothing in the container that would affect vertical position. Tried setting UL/LI padding/margin-top to 0px, making position absolute and setting top:0px. Nowt works. Any bright ideas? Ta.

***Cured by usual random fannying about.