Google Chrome extension (early access) https://chrome.google.com/webstore/detail/plaintextify/emmfeegdeiphciknpfmglmpekijpkann

content_script.js

var res = []

parse(document.documentElement)
chrome.runtime.sendMessage(res)

function parse(node) {
    var i, a, name = node.tagName.toLowerCase()
    res.push({type: 'o', name: name})

    for (i = 0; i < node.attributes.length; ++i) {
        a = node.attributes[i]
        res.push({type: 'a', name: a.name, value: a.value})
    }

    for (i = 0; i < node.childNodes.length; ++i) {
        a = node.childNodes[i]
        if (a.nodeType === Node.ELEMENT_NODE)
            parse(a)
        else if (a.nodeType === Node.TEXT_NODE)
            res.push({type: 't', text: a.textContent})
    }

    res.push({type: 'c', name: name})
}