Best way to locate source of Warning: Empty string passed to getElementById()

Source File: chrome://browser/content/browser.xul

This means that the error is in a Firefox extension, not in your code.

Was receiving this warning in Firefox.

I just came across this warning and found that there were labels for input fields but the labels for attribute was not set/empty so just completing the for attribute fixed this issue for me.

// Label's for attribute not set which caused the warning in FF

e.g. <label for=''>Text</label><input type="text" name="text" id="text" value="" />

If you are querying by '#' selector -- ensure the selector is unique (as it should be) or you will end up with this error in ff

In my case this was caused by Firefox performing HTML5 checks on the input fields on my form. Once the "required" property was removed from the form elements everything seemed to work fine again.

This was something brought about by the MVC framework I use which generates these properties based on the model validation rules that require a field to be non-empty.