MDN = Mozilla Developer Network, one of the best developer resources that not enough people seem to use.
This plugin will let you search MDN either by the word(s) selected or through the command palette and letting you input a search query. Once you enter the query, a browser page opens up with the MDN search results.
Huge thanks to Eric Martel for his SO Search plugin which served as a base for mine, so most of this code is his.
If you're using Package Control (and you should), simply search for "MDN Search" and install it. Done.
Highlight text, right click & click "Search MDN". You can also go through the tools menu. Else, bring up the palette and type "MDN Search" to bring up the options.