Roundcube
Roundcube is a web based mail client.
This is a collection of random ramblings regarding working with it.
Use as mailto provider
The base url is as follows:
https://<host>/?_task=mail&_action=compose&_to=<email address>
To add this to firefox follow the steps outlined in the links below and then use javascript as below:
javascript:navigator.registerProtocolHandler('
mailto,
'https://<host>/?_task=mail&_action=compose&_to=%s',
'Roundcube'
);