http://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html#flash_player_archives
を見ると
http://fpdownload.macromedia.com/get/flashplayer/installers/archive/fp_11.2.202.228_archive.zip
があるので，これをダウンロードして展開．
tonaka@x230% unzip fp_11.2.202.228_archive.zip Archive: fp_11.2.202.228_archive.zip creating: fp_11.2.202.228_archive/11_2r202_223_32bit/ inflating: fp_11.2.202.228_archive/11_2r202_223_32bit/flash_player_11_2r202_228_solaris_x86.tar.bz2 inflating: fp_11.2.202.228_archive/11_2r202_223_32bit/flash_player11_2r202_228_solaris_sparc.tar.bz2 creating: fp_11.2.202.228_archive/11_2r202_228_32bit/ inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_linux.i386.tar.gz inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_linux_sa.i386.tar.gz inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_mac.dmg extracting: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_mac_sa.app.zip inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_win_32bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_win_32bit.msi inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_win_sa_32bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_winax_32bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/flashplayer11_2r202_228_winax_32bit.msi inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/uninstall_flashplayer11_2r202_228_mac.dmg inflating: fp_11.2.202.228_archive/11_2r202_228_32bit/uninstall_flashplayer11_2r202_228_win_32bit.exe creating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/ inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_linux_debug.i386.tar.gz inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_linux_sa_debug.i386.tar.gz inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_mac_debug.dmg extracting: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_mac_sa_debug.app.zip inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_win_debug_32bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_win_sa_debug_32bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_32bit_debug/flashplayer11_2r202_228_winax_debug_32bit.exe creating: fp_11.2.202.228_archive/11_2r202_228_64bit/ inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_linux.x86_64.tar.gz inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_mac.dmg inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_solaris_sparc.tar.bz2 inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_solaris_x86.tar.bz2 inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_win_64bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_win_64bit.msi inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_winax_64bit.exe inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_winax_64bit.msi inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/uninstall_flashplayer11_2r202_228_mac.dmg inflating: fp_11.2.202.228_archive/11_2r202_228_64bit/uninstall_flashplayer11_2r202_228_win_64bit.exe inflating: fp_11.2.202.228_archive/readme.txt
fp_11.2.202.228_archive/11_2r202_228_64bit/flashplayer11_2r202_228_solaris_x86.tar.bz2
というのがあるので，これを使えばよさげ．
展開して，プラグインを ~/.mozilla/plugins に突っ込む．
tonaka@x230% cd fp_11.2.202.228_archive/11_2r202_228_64bit/ tonaka@x230% gtar jxvf flashplayer11_2r202_228_solaris_x86.tar.bz2 flash_player_solaris_11_2_202_223_x86/ flash_player_solaris_11_2_202_223_x86/libflashplayer.so tonaka@x230% mkdir ~/.mozilla/plugins tonaka@x230% cp flash_player_solaris_11_2_202_223_x86/libflashplayer.so ~/.mozilla/plugins/
これで Firefox で Flash が使える．