User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.10) Gecko/20100914 Firefox/3.6.10 Build Identifier: Message filter by Sender should include "reply-to". Reproducible: Always

you mean in the facetted serch (the very html one) ?

I'm not sure what you mean, but it's the filter messages feature, from the "Filter these messages... <Ctrl+F>" textbox.

Quick Filter (per the UI)

We have the same RFE for "All Adresses" (Bug 535879) -> confirming. This RFE has an UX perspective focused on Quick Filter Bar. It's not about message filters or Search messages dialogue (yet). I suppose it's better to handle those separately, if technically possible. We should discuss how this can be realized technically in terms of nsMsgSearchAttributes, and how this should reflect in message filters / Search messages filter options.

I understand that bug 212619 seeks to add the missing nsMsgSearchAttribute for "reply-to" (supported by Mike Cowperthwaite's Bug 212619 Comment 9), and hence is technical prerequisite of this bug.