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Asked: 2026-05-18T05:38:04+00:00

I have some JavaScript code that dynamically injects an iframe in a given HTML

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I have some JavaScript code that dynamically injects an iframe in a given HTML page. Unfortunately, in Firefox, and only in Firefox, although the iframe is created from time to time the relevant URL isn’t loaded into it.

I know it wasn’t loaded because the relevant URL doesn’t appear in the Firebug Net tab, and when I inspect the iframe I don’t see any expected HTML code in there (when the iframe is on the same domain as the outlying page). I don’t see any JavaScript or network errors either.

Here’s a code snippet, I’ve checked all the relevant variables are correct:

    var iframe = document.createElement("iframe");
    iframe.width = options["w"];
    iframe.height = options["h"];
    iframe.scrolling = "no";
    iframe.marginWidth = 0;
    iframe.marginHeight = 0;
    iframe.frameBorder = 0;
    iframe.style.borderWidth = 0;

    if (node.childNodes.length > 0) 
        node.insertBefore(iframe, node.childNodes[0]);
    else 
        node.appendChild(iframe);

    iframe.contentWindow.location = iframeSrc + "?" + querystring;

Here’s an example URL that is set for the iframe (the issue also recreates when the URL points to an external server, had to omit the ‘http://’ at the beginning otherwise I couldn’t post the question):

127.0.0.1:8000/widget/iframe/index.html?style=slide-top-to-bottom&culture_code=en_us&c=26&sc=1324&title=Top%20News&caption=Top%20Stories&order=relevance&count=20&w=250&h=300&timestamp=true&scrollbar=false&theme=ui-lightness&className=8815455464592103&referrer=http%3A%2F%2F127.0.0.1%3A8000%2Fwidget%2Fbuilder%2Findex.html

Doing some research on the web, I found this unfixed Firefox bug which seems related to this issue:
https://bugzilla.mozilla.org/show_bug.cgi?id=279048

After reading the bug, I tried several solutions none of which solved the issue:

  • Setting iframe.src instead of iframe.contentWindow.location
  • Adding a random parameter to the querystring
  • Adding the ‘#’ symbol with a random number at the end of the URL
  • Giving the iframe a random name

Does anyone have a workaround for this annoying Firefox bug? Or is the issue I’m describing unrelated to the bug and has a different solution?

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1 Answer

  1. Editorial Team

    Solved the issue, I was looking in the wrong place. The HTML file where this dynamic iframe was loaded had an empty iframe tag that was removed from the DOM, after which the dynamic iframe was injected instead.

    Apparently Firefox cached the last URL for this iframe, and loaded it immediately as the external page loaded. I know because I saw the relevant HTML file being loaded twice in the Firebug Net tab rather than once upon the injection.

    After I got rid of this empty iframe tag and relied only on the injected iframe, everything started to work well and the issue didn’t reproduce anymore. I guess Firefox didn’t like handling this scenario, some kind of bug maybe?

    Thanks anyway for helping me out, it gave me the inspiration for the right solution 🙂

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