TTSFox от Ett Chung

Text to Speech on Firefox. It use OS build-in TTS engines, you can use it even when offline.
How to use:
1. Click toolbar icon and key-in text, then click "Speech" button.
2. Select text on web page > click mouse right button > click "Speech" item on context menu > click "Speech" button.

When speech, you can click Cancel button to stop speech.