Websockets is disabled in Firefox 4 by default.

The websocket protocol is one of the new HTML5 protocols that implement full-duplex communication between browsers and servers. Traditional browsers only allow interaction with websites through HTTP. However, for rich Web applications such as chat and games, HTTP is not efficient. Therefore, HTML5 provides socket APIs, you only need one handshake to establish a fast channel between the browser and the server.

However, in November 26, security researchers published a research report (PDF), which found that websocket and transparent proxy had serious security problems. They demonstrated cache poisoning attacks based on Upgrade and connect, the researchers proposed to modify the handshake mode. On Bugzilla, Firefox developers discussed this issue. They finally decided that Firefox 4 will not enable websockets by default. Starting from Firefox 4 beta 8, users will need to modify the settings to enable websockets. In the future, Firefox will be enabled by default after security issues are solved.

From: http://www.oschina.net/news/13668/disabling-websockets-for-firefox-4

This article is the use of b3log solo from the simple design of the art of the original article: http://88250.b3log.org/articles/2010/12/10/1291942973503.html