Mark all gmails as read

I use Outlook to revieve emails a lot. Sometimes, especially I'm at work, I also logon my Gmail thru Firefox. I installed the Google toolbar for firefox with Gmail notifier to let me know when a new email coming in.

Here is a problem, using Outlook to recieve emails, the received emails in you account are still shown as unread. So Gmail notifier keep on indicating there are new emails when I restart the firefox, but acutally, they are not really new. So I decided to mark those emails as read, however, it's painful if you have tons of emails unread. 

Google is always my best friend, I found a solution at http://www.woodwardweb.com/technology/marking_all_mai.html   

To mark all mail as read:-

   1. In the search box, type "is:unread"

   2. In the select area press "All"

   3. A link will appear that says "Select all conversations that match this search", press it

   4. From the drop down, select "Mark All as Read".