Emacs as a web browser's external editor
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Since text editing in Emacs is better, Plugins are developed for all major web browsers to use Emacs as their external editor. Mostly these plugins make use of Emacs daemon.
Firefox Family
Iceweasel, Conkeror etc.
Note that Conkeror comes with a small C program that enables external editing of form fields and page source in Emacs. Thus, no third-party extension/plugin is required.
Webkit family
Safari, Chrome etc.