I agree, they should at least enable this plugin on word definition pages. If I want to check out another word I found in the definition I need to switch to a different interface and lose context (I also hate having to do that with my Kindle).
You don't need to switch interfaces to look up words on the Kindle. On my Kindle Keyboard, I can take the caret to just before a word for a quick definition popover. Press return from there to go to the detailed entry on the bundled Oxford Dictionary of English.
In Kindle Touch you touch and hold a word for a second or two but that's beside my point. I want the ability to tap a word or move the caret in the quick definition popover to look up another word within the same interface without having to switch to the full dictionary.
