Do you use Google Docs? If so, you might want to check out the Google Docs Bar for Firefox.

According to the extension website,

gDocsBar is a sidebar extension for firefox, a perfect companion for Google Docs.

With gDocsBar, you can drag and drop multiple files into the sidebar to upload documents.

You can search and filter documents right from the sidebar.

Your Gmail credentials are sent to Google directly over SSL. Your passwords are stored in Firefox Password Manager.

If you use Google Docs, this extension seems like a great idea.