The autocomplete drop down list on form fields (such as the edit box  you enter your search terms) is handy since it remembers data you have entered into them before.  This can save you a bunch of typing, but, if you are like me, you can get annoyed when you have mistyped data in the past or there is something in the history you no longer want there.  

As an example, let us say you were searching on Google for "Microsoft money", but instead, you made a typo and entered "Micrasoft mony".  Every time you type something in the box with a "Mi", you will see that in the drop down list.  While this is no biggy, it can still be annoying (or is to me).  In addition, all those mistyped or no longer needed items it lists makes it slower to find what you are really after.

Another example I find more annoying is when you enter data on a form such as your address.  It is nice to have street, city, name, phone, extra already there in the history, but when you make a mistake sometime, that mistake will always be there in the list which you have to watch out for so that you do not select the mistake.

There is an easy answer that is probably documented somewhere, but if you are like me, you have never read it.  Tonight I thought I would try a couple things and found that you only need to move you mouse over the term in the drop down list and then hit the SHIFT, ALT and DELETE keys at the same time and it will delete the selected item from the list.  

One note though, if you wish to delete multiple items (helps keep the drop down selection cleaner), in FireFox 1.5 at least (may be other versions), you will need to more your mouse off the list and back on the list after each delete for the SHIFT-ALT-DELETE combo to work again for the next term.