Tried and unimpressed by [DeskSMS](https://addons.mozilla.org/en-US/firefox/addon/desksms/).  Claims to be yet another web-service that does what MySMS and MightyText already do very well and that is send text messages from the web as if it was from your phone.  Nothing sets DeskSMS apart.  They claim to have a sweet tablet version but I didn't like it enough to try it out.  Sending texts from a browser and not my phone doesn't happen very often but when it does it's usually with MightyText, MySMS or Google Voice.