Currently less doesn't recognize .txz files, while .tar.xz works fine. $ less foo.txz "foo.txz" may be a binary file. See it anyway? Attached patch fixes this.
Created attachment 244113 [details, diff] mentioned patch
thanks, now in the tree http://sources.gentoo.org/sys-apps/less/files/lesspipe.sh?r1=1.40&r2=1.41