Puntuado con 5 de 5 estrellas

This is a neat little tool :-) I've already found a use for it twice.

However I'm very new to this kind of thing and could really do with a manual or at least a few more details on usage, e.g. how to choose a different icon, how to use the fields in the New Button dialog, etc etc.

Very nice anyway, five stars from me.

Esta valoración es de una versión anterior del complemento (0.9.6). 

Some more info...

button id is just a unique string...
menu/context (fairly tricky) see notes...
icon - any link to resource will do (http/chrome) but if the resource is unavailable (because the add-on is disabled for ex..) you'll get blank button. so the best way is to convert a 16x16 icon to data:image/png;base64...
you can install killspinners add-on and check the samples as an example of for menu, icon usage