Rated 1 out of 5 stars
For all those who (like me) find the new version AWFUL: the instructions on how to downgrade properly can be found here: http://www.ideashower.com/support/read-it-later/how-to-downgrade-from-20-to-09/
If you don't downgrade properly RIL will break. In my case, after a first improper downgrade and a later proper downgrade, the button was gone. Got it back by also resetting in about:config the entry "isreaditlater.added_to_toolbar" (rightclick > "Reset). Button appeared in navigation toolbar again.