firefox不自带flash插件，且提示缺少插件的情况下检测安装也很难成功（我一次也没有成功）。
从adobe flash官网上下载tar.gz版本，解压后有三个文件usr文件夹，libflashplayer.so库文件和readme.txt文本。在readme中详细说明了各个版本的安装步骤，关于tar.gz说明如下：
Installing using the plugin tar.gz:
o Unpack the plugin tar.gz and copy the files to the appropriate location.
o Save the plugin tar.gz locally and note the location the file was saved to.
o Launch terminal and change directories to the location the file was saved to.
o Unpack the tar.gz file. Once unpacked you will see the following:
+ libflashplayer.so
+ /usr
o Identify the location of the browser plugins directory, based on your Linux distribution and Firefox version
o Copy libflashplayer.so to the appropriate browser plugins directory. At the prompt type:
+ cp libflashlayer.so <BrowserPluginsLocation>
o Copy the Flash Player Local Settings configurations files to the /usr directory. At the prompt type:
+ sudo cp -r usr/* /usr
其中重要的是：
（1）找到firefox浏览器插件所在的位置/usr/lib/mozilla/plugins，然后将libflashplayer.so复制到该文件夹中。
（2）把usr文件夹着哦功能的所有文件复制到/usr中，命令sudo cp -r usr/* /usr（root权限）。