Hi,
You can safely install firefox (iceweasle) which will give you spell check while on the forum also
It is smart enough to fire up iceweasle even though the call is for mozilla. You can also install mozilla-thunderbird (icedove) safely. There are few more apps that don't break the main purpose of KM including frozen-bubbles & gnome-games. As long as when you do an apt-get install xxxxx it does not remove files or update files then it is usually safe. The gnome-games does update three libraries however I have not seen any negative side effects, yet. I usually install synaptic so I can "browse" to find the correct names but install directly to better keep an eye on what is happening. Just keep a good current backup so if you hose the system, you can rebuild
Open Office has an issue with only a man page but the man page is part of another package which gives you a chicken / egg loop that will cause a lot of gas.. . so unless you are real handy, don't try that yet cause it will block any further additions.
Mike