I recently added some plugins to FireFox that I love. One is Googlepedia which includes a relevant Wikipedia article with Google and Yahoo search results. Another plugin that plays well with Googlepedia is Google Preview. It adds a thumbnail of the website to the search results.
Another tool I have been using a lot is Gmail This. You can get it by following htis link or clicking on the gmail this link on my sidebar. You just drag the link to your browser bar and when you want to send the link to the website you are visiting you just click gmail this and a new window opens up allowing you to compose and send the email from your gmail account.
Here is a screenshot of Googlepedia and Google preview: