The Edit Page Jetpack feature gives you the ability to edit pages with a single click.
Info
Installing the Edit Page Jetpack feature
If an info bar did not appear at the top of this page asking for confirmation to install the Edit Page Jetpack feature, you need install the Mozilla Jetpack Firefox plugin and then visit this page again after restarting your browser. If you trust me not to do anything malicious with your browser, click the check box for auto-updating this feature while you are on the install page.
Toggle editing mode
Left click on the button in your status bar. It will then appear as and the page in your browser tab currently being viewed will become editable. Click the button again to toggle off editing mode and restore the button to normal.
Toggle spellcheck
Right click on the button in your status bar while the page in your browser tab currently being viewed is in editing mode to toggle spellcheck.
Changing the default spellcheck preference
To change the default spellcheck preference, type about:config into the location bar (if you see a warning page, push the button to proceed) and type extensions.jetpack.features.editpage.spellcheck into the text box at the top of the page. Double click on the extensions.jetpack.features.editpage.spellcheck item to toggle the default spellcheck preference. Setting the preference to true will make spellcheck be on by default while a page is in editing mode. Likewise, setting the preference to false will yield the opposite result, make spellcheck be off by default while a page is in editing mode
Source code
The source code for the Edit Page Jetpack feature is in edit-page.js.