You cannot navigate to the editor controls using the tab key. Although many of these controls are accessible via shortcuts and other means, there should be a means of getting to any control displayed onscreen using the keyboard. Ideally the tab key would focus on the whole panel and the cursor keys would allow navigation within the panel.

This is a failure in meeting Level A of the WCAG 2.0.

For an example of how this has been done well, check out the CK editor: http://ckeditor.com/

For examples on how to do toolbars well, check out this link:

http://test.cita.illinois.edu/aria/toolbar/index.php