User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1b4pre) Gecko/20090407 SeaMonkey/2.0b1pre Build Identifier: 4ade022a670d Error: Component returned failure code: 0x80004002 (NS_NOINTERFACE) [nsISupports.QueryInterface] Source file: ........profile/extensions/%7B340c2bbc-ce74-4362-90b5-7c26312808ef%7D/modules/engines/forms.js Line: 238 it's string let inputElement = element.QueryInterface(Ci.nsIDOMHTMLInputElement); Reproducible: Always Steps to Reproduce: 1. try to submit a form, for example, at forum Actual Results: data not submitted, error in error log generated Expected Results: data should be submitted

QI will throw if the object doesn't implement that interface. Presumably things like <buttons> and <textareas> don't. Checking |instanceof| would be safer, but really this line could just be deleted since you're checking .type right below it. In other news, I don't think the Weave code matches what Satchel is doing any more. eg, http://mxr.mozilla.org/mozilla-central/source/toolkit/components/satchel/src/nsStorageFormHistory.cpp#469 I suspect Weave is generating changes for items that Satchel isn't actually storing. Dunno if/how that would manifest as a problem. You probably want Satchel to fire notifications when it adds/removes/modifies form history items...

http://hg.mozilla.org/labs/weave/rev/792e73ce4f9c Get rid of the QueryInterface and just use instanceof while copying the logic of nsFormHistory::Notify to avoid divergent logic until satchel provides a notification.