There are a couple of reasons why Address AutoComplete may not work.
A few things to check:
- Is the address that you’re typing in your Address Book? If not, it won’t AutoComplete for you.
- Do you have the latest Yahoo toolbar? If not, AutoComplete may not work.
- IE 6.0 and above for Windows
- Firefox 1.x and above for Windows & Mac
Remember, even if you can’t AutoComplete addresses, you can still insert contacts from your Address Book by clicking on the "Insert addresses" or "To:" links on your Compose page.