Two plugins in one browser just makes trouble

Today one website I usually visit requires me to upgrade the Adobe Flash player, and in fact, I just did recently n the emerge world. From the output of the Firefox about:plugins, I seem to have more than one Flash player installed: Two Flash plugins installed in Firefox

It is a little bit overkill to launch strace as Firefox considerately leaves the option to expose the full path by enabling plugin.expose_full_path in about:config, this is the screenshot after netscape-flash-9.0.124.0 is un-emerged:

One Flash plugin installed in Firefox with full path exposed
One Flash plugin installed in Firefox with full path exposed

It seems that I somehow manually installed the flash-7.0r63 in the home directory that overrides the system-wide Flash plugin. Once it is removed, and 9.0.124.0 is re-emerged, everything works.

BTW, if you happen to be a Flash developer, and would need to install multiple versions of Flash player, it is may be worthy taking a look at Flash Switcher as well.