As others have noted, you don't really need to do anything. Modern OSes (not just Linux, Windows too!) aggressively use extra RAM to cache recently used data, and in some cases other data the OS thinks you might access in the near future (pre-fetch). That RAM is already being put to use, making your overall experience smoother.
To see a simple example of how this works, reboot the system then try opening a large application (e.g. LibreOffice). Now close the application, then immediately open it again. You'll notice that the second time it opens much faster (nearly instantaneously). This is because the first time you opened it, the OS fetched it from disk; but the second time, it was still sitting in the file cache from the first time you opened it.
As others have noted, you've also got plenty of RAM to run VMs if you want to try out other distros.
Moving /tmp to a RAMdisk (the tmpfs thing) may help a little with certain apps, but personally I wouldn't bother. Temporary files will automatically take advantage of the extra RAM as cache even if you don't explicitly enable tmpfs, and enabling tmpfs may even hurt in some cases since it will take RAM away from what's available for general file caching.
You should switch to Firefox.
If he wants to use more RAM, that would fulfill his wish.
In a similar vein, he could try running the KDE desktop. I've been evaluating it myself, and there are some things to like, but also some usability issues; and it is a massive memory pig. Currently torn between making a go of KDE, or trying MATE (or even Xfce).