chrome.contextMenus

右クリックで、twitter検索

{
  "manifest_version": 2,
  "name": "My Extension",
  "version": "0.4",

	"description": "twitter search from context menu",

	"permissions": ["tabs", "http://*/*","https://*/*", "contextMenus"],

	"background": {
		"scripts": ["background.js"]
	}
}

chrome.contextMenus.create({
	"title":"「%s」をtwitterで検索",
	"type":"normal",
	"contexts":["selection"],
	"onclick": function(info){
		var url = 'https://twitter.com/search?q='+ encodeURIComponent(info.selectionText);
		chrome.tabs.create({
			url: url
		});
	}
});

ドキュメント
Chrome developer