Rated 2 out of 5 stars
You can only highlight a maximum of two words per page. Not even phrases...if you try to highlight two phrases that occur multiple times on a page then you can only have one phrase highlighted. Its pretty low on features and capability. I don't recommend it.This review is for a previous version of the add-on (0.3.1).
Please contact me
For the record, I can select your string "a maximum of two words per page", choose "Highlight Words" and the behaviour is as expected.
It sounds like you're coming up against a bug or incompatibility with another extension. Please contact me with details and I'll look into it.