Some time ago, I downloaded the latest Tor Browser for Linux and got this weird extension .tar.xz.

tar -xJf tor-browser.tar.xz

You have to install xz-utils package first:

$ sudo apt-get install xz-utils

You can use unxz command to extract .xz files:

$ unxz file.xz

or using with --decompress option of xz:

$ xz --decompress file.xz

Reference: https://linux-tips.com/t/how-to-extract-xz-files/265