I'm sorry its not working for you. Could you send an email to support @ richardfrost.info (without spaces) with your config? You can export your config from Options page > Config tab > Export button. I just double-checked, and it is still working on Twitter for me in Firefox. If you'd rather not share you config, perhaps try saving a copy of your config using the steps outlined above, then reset back to defaults (same page in options) and try it again.

You might also check to make sure it isn't disabled on twitter. You can check that in Options page > domain tab, or by opening the extension's popup on Twitter and making sure the switch is on/blue.