If you are well versed with the position of the keys on your keyboard, and type fairly well, you can improve your typing skills if you are using Mozilla Firefox Browser (the same may be true for Thunderbird and Netscape... I really don't know).
1) Open the webpage (or HTML file or even TXT file) that contains the text that you want to practice typing on.
2) Press Ctrl+F (or click Edit>Find in This Page...)
3) Make sure the cursor is in the text box in the Find bar that appears below. If you want, check "Match case".
4) Find your favorite paragraph and start typing. The paragraph you type will get selected in green according to how much you type. (Note that if the first word of the paragraph is repeated somewhere before it, the paragraph will begin to be selected on completion of second or third word.)
5) When you make a mistake, the paragraph deselects, the Find box becomes red, and a warning appears in the Find bar. Press backspace key until this condition changes back to the normal green selection.
6) When you complete the paragraph, press Shift+Home and press Backspace. (The idea here is to clear the Find text box and prepare it for the next paragraph.)
TIP: If "Edit > Preferences > Advanced > Accessibility > Begin finding when you begin typing" is checked, you can directly go to step 4 after step 1, and the Find bar will appear automatically.
Enjoy your typing and tell me when you become a ninja typist using only Firefox (or whatever)!!