Using GM-scripts with other BrowserGreasemonkey-Scripts are to use with Firefox and Firefox-Addon Greasemonkey.
However, it is possible to use them in other browsers as well (now with videos!):
For firefox, just install greasemonkey-addon here: https://addons.mozilla.org/de/firefox/addon/greasemonkey/
Everything is now set well, just visit the intall-link within the userscripts-description, press install on the targeted site and refresh deviantart to use it!
Brand new Way:
Just install the extension "Violent Monkey": https://addons.opera.com/de/extensions/details/violent-monkey/?display=en
And suddenly everything is as easy as in Firefox!
Just follow the userscript's install link and press the "install" button. A little prompt will show up and suddenly the script is working!
Oldschool (more work for less features):
See the video: http://www.youtube.com/watch?v=AWqeFf6v5R0
If the userscripts aren't using GM_functions, they will work in Opera just fine with copying