abcTajpu – Firefox browser add-on
This enables you to type Esperanto letters and others in Firefox and Thunderbird, either using a context menu or by a keyboard macro. This add-on is available for download here.
Esperanto Toolbar for Firefox
This add-on gives you buttons for typing the 12 accented letters in Esperanto and a search link to Reta Vortaro. You can download it from here.