content_script.js

// Wait for document ready before executing main function
var readyStateCheckInterval = setInterval(function() {
    if (document.readyState === "interactive") {
        clearInterval(readyStateCheckInterval);
        main();
    }
}, 10);

function main() {
    // Replace page title
    document.title = generateReplacment(document.title);

    // Replace all initial text on page
    replaceNodeText(document.body);

    // Create a mutation observer to monitor the DOM for changes
    var observer = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            Array.prototype.slice.call(mutation.addedNodes).forEach(replaceNodeText);
        });
    });

    // Configure and start the observer
    observer.observe(document.body, {
        childList: true,
        subtree: true,
        attributes: false,
        characterData: false
    });
}

function replaceNodeText(node) {

    // Do nothing for nodes contained in a Google Docs editor (sorry I.E. no support for you)
    if(node.closest && node.closest('.kix-appview')) return;

    // Create a tree walker to traverse all text nodes
    var walker = document.createTreeWalker(
        node,
        NodeFilter.SHOW_TEXT,
        {
            acceptNode: function(node) {
                // Reject contentEditable nodes
                return (node.parentElement && node.parentElement.isContentEditable) ?
                    NodeFilter.FILTER_SKIP :
                    NodeFilter.FILTER_ACCEPT;
            }
        },
        false
    );

    // Replace all text nodes
    var textNode;
    while(textNode = walker.nextNode()) {
        textNode.nodeValue = generateReplacment(textNode.nodeValue);
    }
}

function generateReplacment(text) {

    // TODO: perform with a single replace command
    return text
               .replace(/\bFlorida Man\b/g, "Man Likely Suffering From Mental Illness and/or Drug Addiction")
               .replace(/\bFlorida man\b/g, "man likely suffering from mental illness and/or drug addiction")
               .replace(/\bFlorida Woman\b/g, "Woman Likely Suffering From Mental Illness and/or Drug Addiction")
               .replace(/\bFlorida woman\b/g, "woman likely suffering from mental illness and/or drug addiction");

}