WARNING: Most of this content (with the exception of the Mozilla 1.9 XPCOM reference) is very old, and can be expected to be out of date and possibly obsolete. For better XUL documentation, please visit the XUL hub at the Mozilla Developer Center.
How do I put arbitrary elements in a tree?
The short answer is, you don't. Trees are designed to support text content only. This is done for performance reasons, and allows a tree to handle thousands or millions of rows without any performance issues. In fact, a tree with only a few rows can be displayed in about the same time as a tree with a million rows. This is because a tree only needs to handle the rows that are currently displayed.
However, trees do support two special types of content besides text: images and progress meters. Mozilla's download manager uses a progress meter to display the percentage downloaded so far.
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