Installing Java can be a pain on any OS. So, below is my experience getting NEM working in Firefox on Linux Mint, without a browser plugin. This then should work on Ubuntu 14.04 and other similar Linux systems.
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#Download java from java.com
The Free Download link will lead to http://java.com/en/download/linux_manual.jsp?locale=en which suggests [Linux filesize: 61.5 MB] and instructions that I used without success.
Download then that jre-8u25-linux-i586.tar.gz to whever you want, open a terminal and change into that directory.
#Install java to /usr/java (or any other place)
mkdir /usr/java
sudo chown $(whoami) /usr/java
mv ./jre-8u25-linux-i586.tar.gz /usr/java
tar zxvf jre-8u25-linux-i586.tar.gz
#Make java visible from /usr/java (or any other place - just change the /usr/java base below)
cd /usr/local/bin
sudo ln -s /usr/java/jre1.8.0_25/bin/java java
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#Running NEM in Firefox
Download nis-ncc-0.4.12.tgz or whatever is the latest version now from http://bob.nem.ninja/
Extract from nis-ncc-0.4.12.tgz to wherever you want NEM based.
Then open two terminals for each of
./package/nix.runNis.sh
./package/nix.runNcc.sh
Those terminals then give a sense that something is happening, even if that is simple red peppering of errors of no route to nodes. I guess then useful to keep nodes running and the network strong.
After a while NIS will become available and the NEM client will work by visiting http://127.0.0.1:8989 If it's not the first boot, it seems there is a slight delay while it rescans the blockchain it knows. More obvious then is the delay downloading the blockchain it doesn't know.
NIS suggests it is available at http://127.0.0.1:7890 but I have no idea what that should suggest. At the moment to me it appears to suggest only a simple JSON error message.
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Disclaimer: beyond this above, I know little about how NEM works… and I'm stuck five days behind on block 12961 but that's a whole other problem.
Glad to see some Linux people here!
Congrats on figuring out what to do with that *.tar.gz file, as the official instructions on java site weren't very helpful. I decided not to bother with it and found an automated java installer, which seemed to do the job. Here is my experience: https://forum.ournem.com/index.php?topic=2602.0
Regarding NEM client getting stuck at some block, happened once or twice to me as well. I just let it sit there for a few minutes and managed to get through. There were explanations from the devs, that some scripts created bottlenecks at certain points in the blockchain and NEM client had a hard time processing those transactions very quickly.
Hello fellow linux nemer 
Thanks for the info!
I'm also using latest NEM standalone package release on linux but I left the system "original" java 7 on it.
I have installed java 8 (the targ.gz file) in a folder on the system by extracting it
and changed the .sh scripts (start NIS and start NCC) in the NEM package to point into that bin folder where java 8 is located.
So instead having this in the files:<br />java -cp "...<br />
i have<br />/path_to_java_8_folder/bin/java -cp "...<br />
I' m starting the NIS and NCC from command line entering this "./nix.runNis.sh" and "./nix.runNcc" but
before i do that I change the dir to "path to NEM package".
..and changed the .sh scripts (start NIS and start NCC) in the NEM package to point into that bin folder where java 8 is located.
So instead having this in the files:
[code]
java -cp "...
[/code]
i have
[code]
/path_to_java_8_folder/bin/java -cp "...
[/code]
..
Yes, I did that initially too but fixing those scripts at each update might become a pain.
The [#Make java visible] above, does the same but you only need to set up that java pointer once.
The only downside might be if you really do prefer using java7 for other applications.
Below worked for me, which I used from this site.
http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html
LINUX terminal:~$
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer