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Editorial Team
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Asked: 2026-05-27T21:57:38+00:00

For example, in the following HTML … <form name=outerform> <input type=text name=outer1/> <input type=text

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For example, in the following HTML …

<form name="outerform">
  <input type="text" name="outer1"/>
  <input type="text" name="outer2"/>

  <div>
    <form name="innerform" method="post" action="#">
      <input type="text" name="inner1"/>
    </form>
  </div>
</form>

Firefox will simply throw away the innerform <form> tag, since forms cannot be nested.

I ran into this while patching some legacy code. Someone had placed a <form> tag covering almost the entire body content. When I added my own, more localized <form>, Firefox stripped out the inner tag and my submits were going to the outer form. Since I was doing some jQuery processing to create my submit URL, I thought it was my error. I realized the problem after viewing the rendered HTML in Firebug’s HTML tab.

If the browser, or Firebug had a tab for “ignored HTML”, or some such method I would have picked it out immediately. I can’t simply do a View-Source and paste it into the W3C’s web-based validation service for the following reasons:

  1. For security reasons, the development computer I’m on is not connected to the public Internet.
  2. Firebug’s HTML tab shows the rendered HTML, so the invalid HTML tag has already been removed.

Finally, the editor (Eclipse) is usually where I catch bugs like this. But we use a lot of included files and the Tiles framework, so you only see a fragment of the final HTML page at a time.

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1 Answer

  1. Editorial Team

    I found my solution. Thanks to Boris Zbarsky’s comment for pointing me in the right direction. The view-source shows the downloaded HTML, but the Firebug DOM inspector shows the rendered HTML (I was mistaking the two in the question). Solution:

    1. Do a view-source and save the file (File 1)
    2. Open Firebug’s DOM inspector, right-click the top-level element <html>, Copy HTML, and save to file (File 2)
    3. Use a diff tool to compare the two files. In a graphical diff tool, File 2 will show gaps where the browser ignored/removed HTML.

    Reformatting the HTML in the two files might make diffing easier.

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