The tab key does not behave intuitively when composing a message.
Most people expect that pressing the tab key will insert a tab (or x number of space characters). However, instead of spacing, it moves the focus.
This is entirely understandable, but it would be nice to have a mechanism to insert tabs within an email instead of counting spaces.
The bulleted list and numbered list work for certain scenarios, but not all. Perhaps a button on the composition toolbar that will act as a tab key would be useful?
Anyhow, I found a Bugzilla entry about this (Bug 9744). If anyone would like to see this implemented, please vote for the enhancement.