Internet Text Speaker is a plug-in for both Internet Explorer and Mozilla Firefox which lets you, via a voice synthesizer, read any text you select.
To activate Internet Text Speaker you just have to select a text from a webpage and right click on it to access the contextual menu. In that menu you can access the diverse options of the voice synthesizer so it reads the selected text. The user can adjust the volume, type of voice, reading speed, etc.
Internet Text Speaker is totally free.