If you decompressed it, it likely went into a directory named "firefox-27.0" inside the directory where it resided when you decompressed.
Not being able to see your computer, I am not able to offer keystroke by keystroke instructions.
If you are running Knoppix as a Live Distro, have you enabled persistance
? If not, any changes you make will be lost.
Regarding commands, yes, Linux commands are different, though there is a lot of overlap. If you do a web search for "Linux commands quick reference," you will find many resources. Here's one: http://oreilly.com/openbook/debian/book/appe_01.html
I'm curious. Why are looking to install a newer Firefox in Knoppix?