The error should indicate some missing content in external software which is accessible through the link provided (and probably in any browser), so not internally from Firefox or one of any installed add-ons.

I’m not familiar with the product, but you could try uninstalling and reinstalling the latest software for the Web LCT component as found here. You could also uninstall what you no longer need.

The above may not be right.

This is not entirely my area of expertise but when searching for the error message, several threads and possible causes can be found - one of them describing them is this thread.

Quotes: "I figured a little bit out - turns out the error is a FireFox error when it gets an empty document and is expecting XML." "i believe it's a firefox caching issue. but the underlying problem is that the page is not rendering anything." "this actually is a firefox issue. if you view source, you'll see that there's no output. If you were to view the site in another browser, you wouldn't see this error."

So my bet is some server software (Web LCT?) isn’t running properly or unreachable for some reason (port busy) and you get no data, resulting in the error. As posted in the thread, it’s a side effect.

If you search Bugzilla for "XML parsing error", you’ll find a number of open bugs that may be helpful.

Hope this helps.