起初是访问了某个需要有adobe flash player的主页，结果页面显示需要安装插件，然后我就点了页面上的安装，过程倒是很顺利，一会就装完了，但是无论重启firefox还是还是电脑，刚才装完的插件都没有起作用。
然后就一顿搜索，最后使用下面的安装命令，装完后重启firefox起作用了。
zz@zz:~$ sudo apt-get install flashplugin-installer
[sudo] password for zz:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
linux-headers-4.15.0-60 linux-headers-4.15.0-60-generic linux-image-4.15.0-60-generic linux-modules-4.15.0-60-generic
linux-modules-extra-4.15.0-60-generic
Use 'sudo apt autoremove' to remove them.
Suggested packages:
x-ttcidfont-conf ttf-mscorefonts-installer ttf-bitstream-vera | ttf-dejavu ttf-xfree86-nonfree xfs
The following packages will be REMOVED:
adobe-flash-properties-gtk adobe-flashplugin
The following NEW packages will be installed:
flashplugin-installer
0 upgraded, 1 newly installed, 2 to remove and 148 not upgraded.
Need to get 6,778 B of archives.
After this operation, 36.2 MB disk space will be freed.
Do you want to continue? [Y/n] y
Get:1 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 flashplugin-installer amd64 32.0.0.255ubuntu0.16.04.1 [6,778 B]
Fetched 6,778 B in 0s (8,126 B/s)
Preconfiguring packages ...
(Reading database ... 263946 files and directories currently installed.)
Removing adobe-flash-properties-gtk (1:20181120.1-0ubuntu0.16.04.1) ...
Removing adobe-flashplugin (1:20181120.1-0ubuntu0.16.04.1) ...
Processing triggers for gnome-menus (3.13.3-6ubuntu3.1) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu5.2) ...
Processing triggers for bamfdaemon (0.5.3~bzr0+16.04.20180209-0ubuntu1) ...
Rebuilding /usr/share/applications/bamf-2.index...
Processing triggers for mime-support (3.59ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.15-0ubuntu1.1) ...
Selecting previously unselected package flashplugin-installer.
(Reading database ... 263916 files and directories currently installed.)
Preparing to unpack .../flashplugin-installer_32.0.0.255ubuntu0.16.04.1_amd64.deb ...
Unpacking flashplugin-installer (32.0.0.255ubuntu0.16.04.1) ...
Processing triggers for update-notifier-common (3.168.9) ...
flashplugin-installer: processing...
flashplugin-installer: downloading http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20190910.1.orig.tar.gz
Get:1 http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20190910.1.orig.tar.gz [30.6 MB]
Fetched 30.6 MB in 4min 11s (122 kB/s)
Installing from local file /var/lib/update-notifier/package-data-downloads/partial/adobe-flashplugin_20190910.1.orig.tar.gz
Flash Plugin installed.
Setting up flashplugin-installer (32.0.0.255ubuntu0.16.04.1) ...
zz@zz:~$