Javascript in 4chan 404 defeater

4chan 404 defeater is a Firefox extension used to auto refresh 4chan threads in Firefox until they 404 (without showing a 404 screen):
Website:
http://spacetaken.net/44d/

Firefox extension:
http://spacetaken.net/44d/4chan404defeater_0-4.xpi

Greasemonkey script:
http://spacetaken.net/44d/4chan404defeater_0-4.user.js

Inside that .xpi is chandefeater.js and it's identical to the Greasemonkey script. I've been using 4chan 404 defeater for a while and I don't know anything about Javascript.

I want to modify that .js so instead of the default (auto F5'ing turned off (unchecked) and refresh rate set at every 2 minutes), I want the default to be checked and 8 minutes.

From window.saveCookies, it evidently saves a cookie for each open tab, saving the scroll position (44d_scroll_pos), the F5 interval (44d_f5_rate), and whether auto F5'ing (44d_auto_f5) is on/checked/true or off/unchecked/false.

I can view those cookies in Firefox through Tools > Options > Privacy > Show cookies and doing a Search for 4chan.

If I edit the .js and change:
var autoF5Rate = readCookie("44d_f5_rate", 2);
to
var autoF5Rate = readCookie("44d_f5_rate", 8);
..that changes the default refresh rate to 8 minutes.

But if I change:
var autoF5 = readCookie("44d_auto_f5", false);
to
var autoF5 = readCookie("44d_auto_f5", true);
..it does nothing.

The terms "checked" and "auto_f5_checker" both appear 6 times in that .js

The term "document.getElementById("auto_f5_checker").checked" appears 3 times in that .js

I think it has something to do with "onlick" and ".checked"

I'm currently focuses on these portions of code:

unsafeWindow.updateAutoF5 = function(){
    var checked = document.getElementById("auto_f5_checker").checked;
    //stop or start auto f5ing
    if(checked)
        autoF5TimerId = setInterval('doF5()', 1000*60*autoF5Rate);
    else
        clearInterval(autoF5TimerId);
}

unsafeWindow.validateRate = function(){
    var field = document.getElementById("ref_rate_mins");
    autoF5Rate = parseFloat(field.value);
    if(isNaN(autoF5Rate)) autoF5Rate = 1;
    else if(autoF5Rate < 0.1) autoF5Rate = 0.1;
    field.value = autoF5Rate;        //update to possibly different-to-inputted value
    if(document.getElementById("auto_f5_checker").checked){
        clearInterval(autoF5TimerId);
        autoF5TimerId = setInterval("doF5()", Math.round(1000*60*autoF5Rate));
    }
}

window.saveCookies = function(){
    writeCookie("44d_scroll_pos", document.body.scrollTop);
    if(document.getElementById("auto_f5_checker")){
        writeCookie("44d_f5_rate", autoF5Rate);   
        writeCookie("44d_auto_f5", document.getElementById("auto_f5_checker").checked);
    }
}

How do I make it so auto F5'ing is turned on by default in that .js but can still be turned off by unchecking the box (created by window.controlNode)?

All this "404 defeater" crap does not keep threads alive.
i.e. a simple autobump script > refresh tab each x seconds.