You can make all the text on any web page temporarily editable right in the browser. All you need is a browser that has a JavaScript console, which is pretty much all of them nowadays. In Safari, the JavaScript console is accessed with the Show Error Console command in the Develop menu. If you don't see the Develop menu, you have to enable it in the Advanced tab of Safari's preferences.
To make a web page editable, open the console and enter the following statement:
document.body.contentEditable = true
Now, when you click on a text element on the page, you will see a standard text cursor. You can add and delete text to your heart's content.
To make the page uneditable again, enter this in the console:
document.body.contentEditable = false
Note that any edits you perform with this trick are strictly temporary; if you reload the page, your edits will vanish. However, you can save the page locally after editing it, if you need to preserve a copy of your edits. Be sure to save it as a 'web archive,' not as 'page source.'
[crarko adds: I tested this, and it works as described.]

