https://addons.mozilla.org/en-US/firefox/addon/qwiki/
(more images can be found there)
alt+lmb (alt key pressed + left mouse button) searches for the full Wikipedia article of the 'clicked' word (in your default language)
alt+shift+lmb for the short article (just a small part of the full)
alt+ctrl+lmb for the tabelaric part of the article
alt+w shows/hides the search input box
"USA" searches for the Wikipedia article 'USA' in your default language
"de:USA" searches for the Wikipedia article 'USA' in german
"ru:USA" searches for the Wikipedia article 'USA' in russian
"de:2:USA" searches… and displays the short version
"de:3:USA" searches… and displays the tabelaric information
"en:?:sky" searches wiktionary.org for the english article about the word 'sky'
"de:?:sky" searches wiktionary.org for the german article about the (english) word 'sky'
"de:?:Himmel" searches wiktionary.org for the german article about the word 'Himmel' (english: sky)
"pl:piorun" searches the polish Wikipedia for 'piorun'
in Firefox click the puzzle symbol
then the gear symbol
switch from details to preferences and select your default language in the dropdown.
you might also change your click-combinations here by just holding your key (alt,shift,ctrl) + pressing a mouse button (lmb,mmb,rmb)
inside one of those fields showing the combination (next to complete, short, wikitable)