To report a bug or to make a suggestion regarding this application or this manual, use the bug tracking system at http://bugzilla.xfce.org/. Remember that useful bug reports are ones that get bugs fixed, so a useful bug report has two qualities:
Reproducible. If the developer cannot see the bug himself to prove that it exists, he will most probably not be able to fix it at all. Every detail you can provide helps.
Specific. The quicker the developer can isolate the problem to a specific area, the more likely he will expediently fix it.
In case you want to request a new feature, please make clear why you consider it a worth addition for the application. It is more likely that a new feature gets added if you provide good arguments for the feature. It will increase the chance of addition even more if you provide a patch that implements the requested feature, but make sure that you read the file HACKING - especially the section labeled Coding Style - before you start hacking up the source.
Else, if you have questions about the use or installation of this software, please ask on the thunar-dev mailing list or point your IRC client to irc.freenode.net, join the channel #thunar and ask for help.