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Rated 4 out of 5 stars
Doesn't really work, at least, not in all cases. Unwanted content is being pushed to the copied text anyway. Try to copy text here: http://www.rosbalt.ru/ukraina/2012/11/14/1058886.html or here:http://liga.net/opinion/84041_tamozhennyy-soyuz-diktatorov-v-chem-zabluzhdaetsya-zapad.htm
UPDATE: See dev's comment below
These pages don't intercept copy/paste events - they simply inject hidden text into the page whenever you select something. Too bad that Firefox still copies hidden text.