Nice! Rated 5 out of 5 stars

Just great! Tip: to highlight multiple words, hold Control when you click on "Highlight word".
It also works fine in 7.0 (Aurora channel); disable the compatibility check by going to about:config and creating a new boolean extensions.checkCompatibility.7.0a = false.

This review is for a previous version of the add-on (0.3.4.1-signed.1-signed).