You can follow these directions and read up on it here:
Most relevant section, and to quote just in case of a dead link:
The solution consists in telling Opera to not use /opt/netscape/plugins/libflashplayer.so. This can be done in three ways:
Solution 1: Preferences -> Advanced -> Downloads ->
application/x-shockwave-flash swf -> Edit... -> Select the correct plugin at
"Use plug-in" drop-down (if more than one is displayed, select any one that does not contain "netscape" in path). Repeat this for application/futuresplash spl file
type. There is no need to restart Opera after this change.
Solution 2: Manually edit ~/.opera/opera6.ini while Opera is closed and change the paths.
Solution 3: Add "/opt/netscape/plugins=2" to ~/.opera/pluginpath.ini.
I used solution #3 to solve it. YMMV.
Tell me how it works.