DOM appendChild error in Gecko 2.0

Blake Winton

I was recently modifying an add-on for the upcoming Thunderbird 3.3, and part of what I wanted to do was to run some javascript in a chrome context that added some DOM nodes to a document in a content context. But when I ran the following code:

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let browser = document.getElementById('tabmail').getBrowserForSelectedTab();
let doc = browser.contentDocument;
dump("\n\n\n\nXXXXXXXXXX\n");
dump("DOM Content loaded for " + doc.location + "\n");
var topBar = document.createElement("div");
topBar.innerHTML = "We got it!!!!!";
dump("iB = "+doc.body.insertBefore+"\n");
dump("fC = "+doc.body.firstChild+"\n");
doc.body.insertBefore(topBar, doc.body.firstChild);

I got the following error:

WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80530009: file /Volumes/Devel/thunderbird/src-central/mozilla/content/base/src/nsNodeUtils.h, line 304
WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80530009: file /Volumes/Devel/thunderbird/src-central/mozilla/content/base/src/nsGenericElement.cpp, line 4077
-- Exception object --
[snip…]
+ message (string) 'Operation is not supported'
+ result (number) 2152923145
+ name (string) 'NS_ERROR_DOM_NOT_SUPPORTED_ERR'

Poking around a little, it seemed like I had reasonable things for the insertBefore method, the firstChild attribute, and the topBar variable, and so since it was late, and I couldn't see what I had done wrong, I went to bed.

That turned out to be a the best thing for me to do, because this morning Jonathan Protzenko came to the rescue, saying (in response to a similar problem with a Firefox 4.0 beta 7 extension):

If you're modifying some content DOM from chrome code, you need to make sure the child you're appending was created using the unprivileged document, not the global document.

// This is chrome code, this is wrong because the span is now chrome
// and you're trying to insert it into content
myContentNode.appendChild(document.createElement("span"))

// This is right, appending a content node to another content node
myContentNode.appendChild(myContentNode.ownerDocument.createElement("span"))

I've hit this issue at least three times when upgrading stuff for Gecko 2.0. Might be what you're looking for .

And sure enough, when I changed var topBar = document.createElement("div"); to var topBar = doc.createElement("div"); , it all started working beautifully.

Thank you, Jonathan!