Sometimes I like to be able to write an email without seeing the new messages in my inbox. This AppleScript (triggered with LaunchBar of course) solves this problem. It opens a new Safari window directly to FastMail's compose page.
Because FastMail loads so quickly and Safari is generally pretty fast fast, this is essentially the same speed of LaunchBar's "Compose Email" action for Mail.app.
tell application "Safari"
make new document with properties {URL:"https://www.fastmail.com/mail/compose?u=FILL_IN_FROM_FASTMAIL_URL"}
activate
end tell