In Page Lookup v2.1.3
In Page Lookup is an extension that lets you look up a word on almost any page without needing to open a new tab.
To look up a word on Wikipedia just highlight the word and right click and choose "InPageLookup" and a sub-option.
An easier way to do it though is to click a combination of keyboard characters (default: ControlLeft+AltLeft+1) and an overlay of the Wikipedia article will appear as an in-page overlay.
To look up a word on Wiktionary just highlight the word and click a combination of keyboard characters (default: ControlLeft+AltLeft+2 ) and an overlay of the Wiktionary article will appear as an in-page overlay.
To close the overlay just highlight the word and click a combination of keyboard characters (default: ControlLeft+AltLeft+`, the key to the left of the '1' key if you have a different keyboard that doesn't have the ` key)
To change these keys, go to the tools/options dropdown and click "Extensions", find the "InPageLookup" one and click on it and then click "Options". Make sure you click save when you are done.
I do not, in anyway, track anything you do, the permissions that are necessary are necessary in order to show the Wiki information. You can see the source code at https://github.com/TheOtherRealm/InPageLookup if you have any misgivings.