Lotus Notes does not function for mail 'send' commands when opened within Firefox.
Lotus Notes functions for email inbox and read functions, but the send, send and file commands do not function after a message has been composed to send, nor can the message be saved as a draft.
Wšykne wótegrona (3)
As a temporary workaround, you can use the 'lite' mode.
This is a known bug : FF no longer support signed scripts. Some settings need to be changed on the server side.
Not the best solution but I reinstalled Firefox 15. Now Lotus Notes works fine including the "send" button".