I did the following to get (linux) flash7 to work in Firefox on FreeBSD 6.0-RELEASE:

- Install www/linuxpluginwrapper
- Install www/linux-flashplugin7
- Put following in /etc/libmap.conf

  [/usr/X11R6/lib/linux-flashplugin7/libflashplayer.so]
  libpthread.so.0                 libpthread.so.2
  libdl.so.2                      pluginwrapper/flash7.so
  libz.so.1                       libz.so.3
  libm.so.6                       libm.so.4
  libc.so.6                       pluginwrapper/flash7.so

- Apply the patch at http://people.FreeBSD.org/~nork/rtld_dlsym_hack.diff to /usr/src/libexec/rtld-elf/rtld.c:
 
  cd /usr/src/libexec/rtld-elf/
  fetch http://people.FreeBSD.org/~nork/rtld_dlsym_hack.diff
  patch < rtld_dlsym_hack.diff
  make clean cleandir
  make clean cleandir (yes, twice!)
  make obj
  make depend
  make
  make install

- Link the plugin:

  ln -s /usr/X11R6/lib/linux-flashplugin7/libflashplayer.so /usr/X11R6/lib/browser_plugins/