You can use WebTools, it's an addon that gather the most useful and basic tools 
such as a synonym dictionary, a dictionary, a translator, a youtube convertor, 
a speedtest and many others (there are ten of them).
You can access them in two clics, without having to open a new tab 
and without having to search for them !

-Chrome Link : 
https://chrome.google.com/webstore/detail/webtools/ejnboneedfadhjddmbckhflmpnlcomge/

Firefox link : https://addons.mozilla.org/fr/firefox/addon/webtools/