I'd like to request a quick filter using the 'Reply To' field, instead of the
'From' field. I get many responses from Kijiji (Local classifieds site), all of
which come from the email post@kijiji.ca. The 'Reply To' field would contain
the customer's email address. I want to be able to drag an email to another
folder, and have it create a filter such that all future emails with the same
'reply to' field would be sent to the same folder.

Accepted, but reclassified as enhancement (new feature request). I think this
is definitely going to be of value. Did you test whether you can add the
reply-to condition manually using the "FiltaQuilla" extension?

I understand this is one part that quickFilters would have to offer (a
drop-down choice for "Reply-To" in the filter conditions). The template would
then fill this automatically when creating the filter from the email.

Created an attachment (id=7948) [details]
2.7.1 prerelease 95

Finally managed to make the reply-to text field visible. 

In order to use the feature now, the following value in about:config must be
toggled (I am leaving this feature as unofficial for 2.7.1)

extensions.quickfilters.experimental.replyTo = true

This shall be a "hidden" feature for the 2.7.1 maintenance release and then 
properly documented when 2.8 will be officially released. Please test
relentlessly before then!

(In reply to comment #2)
> Created an attachment (id=7948) [details] [details]
> 2.7.1 prerelease 95
> 
> Finally managed to make the reply-to text field visible. 
> 
> In order to use the feature now, the following value in about:config must be
> toggled (I am leaving this feature as unofficial for 2.7.1)
> 
> extensions.quickfilters.experimental.replyTo = true
> 
> This shall be a "hidden" feature for the 2.7.1 maintenance release and then 
> properly documented when 2.8 will be officially released. Please test
> relentlessly before then!
> 

Will be released in the next version - this might be marked as a premium
feature, not sure yet. Anyway going forward from version 2.9pre76 I changed the
config setting to 

extensions.quickfilters.templates.replyTo

there will be a checkbox "Reply-To Template" on the quickFilters Preferences >
"Advanced Tab" to make enable this and the template visible...

Implemented: Version 2.8 - 14/12/2014