TypeError: elem.dispatchEvent is not a function on upload

[alancolyer]

Note - this only seems to occur when using Firefox, and Firebug is open.
Tested on Mac OSX 10.7.5 with FF 28.0 and latest Firebug.

When selecting a file or dropping on to the droppable area, the image element loads and the upload starts, but firebug reports the error: TypeError: elem.dispatchEvent is not a function, usually about 20 times.

The script appears to stop, however the upload is actually completed and the response is received but as the script has stopped it looks like the upload hasn't finished.

I asked this question on stackoverflow: http://stackoverflow.com/questions/19543540/debug-strategy-for-javascript-typeerror-elem-dispatchevent-is-not-a-function

The answer suggested an issue with Firebug, documented here: http://code.google.com/p/fbug/issues/detail?id=5939

But the only time I have ever seen this issue is when using jquery-filedrop. Does anyone see the same behaviour, or have a workaround?