You probably noticed that during browsing the Internet with Firefox, several website gave you a message similar to the example below:

"Additional plugins are required to display all the media on this page. Click Install Missing Plugins."

That means your Firefox web browser does not have plugins required by the webstie. It offers you to install the plugins . You can install the plugins just by clicking on the "Install Missing Plugins" button in windows operating system. In Linux, you cannot do that. Linux protected itself with permissions. Here is what happened when you click the Install Missing Plugins button:

The Firefox Plugin Finder Service offers to install the plugins for you. Click Next to install those plugins.

The process completed with no plugins installed. But we know now that the missing plugin is Adobe flash player. So we can manually download flash player from Adobe website and install the plugin. Here is Adobe flash player download page for Linux if you need it: Adobe flash player for Linux download page.

Choose Manual Install and click Finish.

Adobe Flash Player download page opened.

Click Select version to download... dropdown button and choose .tar.gz for Linux. Next, click Agree and install now button.

Choose Save file and click OK.

Open Slackware Linux command line terminal and type su - and enter root password.

Note:

The new 'install_adobe_flash_player_10.tar.gz' has changed. See instruction update at the bottom of the article.

Type cd /usr/local/src and press enter. Untar Adobe flash player 10 with tar zxvf /path/to/install_adobe_flash_player_10.tar.gz command. See the step by step example below:

root@slackware:/home/luzar# cd /usr/local/src 
root@slackware:/usr/local/src# tar zxvf /home/luzar/install_flash_player_10_linux.tar.gz 

Change directory into the new extracted folder with command cd install_flash_player_10_linux. See an example below:

root@slackware:/usr/local/src# ls 
install_flash_player_10_linux/
root@slackware:/usr/local/src# cd install_flash_player_10_linux/

Run flashplayer-installer* like the example below:

root@slackware:/usr/local/src/install_flash_player_10_linux# ls 
flashplayer-installer*  libflashplayer.so*
root@slackware:/usr/local/src/install_flash_player_10_linux# ./flashplayer-installer 

The flash player installation starts. You need to answer a few questions during the installation. So stay put. It only takes a few seconds. See the example below:

Copyright(C) 2002-2009 Adobe Macromedia Software LLC.  All rights reserved.

Adobe Flash Player 10 for Linux

Adobe Flash Player 10 will be installed on this machine.

You are running the Adobe Flash Player installer as the "root" user.
Adobe Flash Player 10 will be installed system-wide.

Support is available at http://www.adobe.com/support/flashplayer/

To install Adobe Flash Player 10 now, press ENTER. 

To cancel the installation at any time, press Control-C.

We want to install Adobe flash player, so press enter to continue. The Adobe flash player will ask for the installation path of the Mozilla, Netscape, or Opera browser. In Slackware, the path should be in /usr/lib directory by default. Enter the name of web browser you are using and press enter to continue. See an example below:

Please enter the installation path of the Mozilla, Netscape,
or Opera browser (i.e., /usr/lib/mozilla): /usr/lib/firefox 
Proceed with the installation? (y/n/q): y 

Installation complete.

The Adobe flash player will ask again whether we want to perform another installation. It means, if we have many web browser in our Linux operating system, we can install Adobe flash player for that browser too. Answer y if we want to install Adobe flash player for other web browser, such as Seamonkey or Opera. Once again, provide the path to the seamonkey web browser. Answer y to continue the installation. If you want to install Adobe flash player to other web browser, repeat the step above. If not, answer n to the Perform another installation question. The step by step example is shown below:

Perform another installation? (y/n): y 

Please enter the installation path of the Mozilla, Netscape,
or Opera browser (i.e., /usr/lib/mozilla): /usr/lib/seamonkey 

----------- Install Action Summary -----------

Adobe Flash Player 10 will be installed in the following directory:

Browser installation directory = /usr/lib/seamonkey

Proceed with the installation? (y/n/q): y 

Installation complete.

Perform another installation? (y/n): n 

Please log out of this session and log in for the changes to take effect.

The Adobe Flash Player installation is complete.

The Adobe flash player installation in Slackware Linux is complete. Login from a new terminal as a normal user and start kde (if kde is not opened already). Open Firefox and test the new Adobe flash player with youtube video to see does it work or not. Do the same test for Seamonkey web browser.

Update!

The new 'install_flash_player_10_linux.tar.gz' file contains only 'libflashplayer.so' file when you extract it. What you need to do is just copy the libflashplayer.so file to the /firefox/plugins directory (and other web browser as well). Here's the complete 'howto' steps:

1. Download 'install_flash_player_10_linux.tar.gz' from adobe website.
2. Extract it when the download is finished. The command is tar zxvf /path-to/install_flash_player_10_linux.tar.gz.
3. Copy 'libflashplayer.so' to /usr/lib/firefox-3.X.XX/plugins directory. Here is the command example: cp /path-to/libflashplayer.so /usr/lib/firefox-3.0.13/plugins.
4. Open Firefox web browser. Type about:plugins to verify flash player.

That's all.