There is a pack of FireFox/GreaseMonkey's scripts for English learners.
-
Cambridge (obsolete since they changed html)
Show the British meaning of word by double click or F1. -
LinguaLeo
Translate word by double click or F1 for a selected text.
If the word is not found then the Yandex translation will be shown.
There is no Yandex translation since Yandex stopped free access to API.
You should login on LinguaLeo site in a browser. -
Notebook.js
Simple words and phrases store.
Use F2 to add item and Ctrl + F2 to show/hide item list.
Watch the video to learn more