Rated 3 out of 5 stars
I have used, and LOVED, this extension for the past couple of years. Sadly it's now kaput... doesn't work with the latest version(s) of Firefox.
So, the good news... get Chrome then download the extension I wrote this week which gives you the same result! :)
In case the link I pasted below is stripped out automatically, Google for the phrase "google view page as text extension" and you should find it near the top. Source code is available for anyone that wants to port it to a FireFox add-on as well.