How do I fix Flash issues?

As you have identified - the best solution is usually to follow this Q&A to install flash. It does work for the vast majority of users.

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Flash-Aid was discontinued by it's author and is unknown if it will be back, the following are kept only for historical reasons.

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As an alternative, one of the best tools I have found that allows you to configure Flash correctly during installation is the Flash-Aid addon - use the author's site or search on the Firefox addon-manager for Flash-Aid

This will remove any remnants of of Flash installation and install flash directly from the Adobe Website. During the wizard installation you have a few configuration options that you can try to resolve flash-player issues.

Close & Restart Firefox / reboot for the change to take effect.

See also:

• Why are Flash applications so sluggish/crashy?

There are 2 options.

Enable the HTML5 player

For Youtube this can be done by loggin in, going to http://www.youtube.com/html5 and enabling it there. You can also just add &html5=True behind each video URL.

• There is a trick for the cases when there appears to be no HTML5 option available on YouTube: use the "embedded" variant.

  For example: https://www.youtube.com/watch?v=3SacL219sic&html5=True appears to be not watchable in HTML5, but https://www.youtube.com/embed/3SacL219sic plays in HTML5!

Whether your browser and the version you are using will support the HTML5 playback of a video on a site that provides such an option (like YouTube or VKontakte) will depend on the codec chosen by the site owners. For example, YouTube and VKontakte (a Facebook clone popuar in Russia) use different codecs for their HTML5 videos, which means that in Ubuntu 12.04 HTML5 video playback at VK.com works in Chromium, but not in Firefox (and in future, these browsers might swap their roles).

Install the Flash Aid Firefox plugin

I don't know for sure if this will work for you as well, but it worked for me.
Install Flash Aid, restart Firefox, and click the Flash button at the upper right corner of Firefox's window. Just follow the instructions in the wizard and you should be fine.

For some more detailed guide on installing Flash using Flash Aid, check out fossfreedom's answer: https://askubuntu.com/a/86260/18953

For Firefox Flash, first try this:

when having issues after an automatic update.

$ sudo apt-get --reinstall install flashplugin-installer

This leaves one with Adobe Flash plugin version 11.2.???.??? in Firefox as Adobe no longer releases any higher flash versions for Linux.

For the moment, the 11.2 series of the Adobe Flash plugin for Linux is still maintained and security updates will trickle in automatically. However, one will miss out on innovations and power efficiency improvements.

For adding the Google Chrome Pepper Flash plugin to Chromium:

$ sudo add-apt-repository --yes ppa:skunk/pepper-flash
$ sudo apt-get update
$ sudo apt-get install pepflashplugin-installer
$ echo '. /usr/lib/pepflashplugin-installer/pepflashplayer.sh' |sudo tee -a /etc/chromium-browser/default

The latest and greatest Adobe Flash version for Chrome (version 12.0 at the time of writing) is installed in Chromium.

This solution can also be scripted for easy installation on multiple machines:

#!/bin/bash
sudo add-apt-repository --yes ppa:skunk/pepper-flash
sudo apt-get update
sudo apt-get install pepflashplugin-installer
STRING='. /usr/lib/pepflashplugin-installer/pepflashplayer.sh'
FILE='/etc/chromium-browser/default'
if ! grep -qe "$STRING" $FILE
  then
    echo "$STRING" |sudo tee -a $FILE
fi

Unlike Firefox Flash, Pepper Flash is not updated automatically by the update manager; it requires a tedious manual process. Forgetting about this leaves one exposed to security threats.

Here is another bash script to render manually updating Pepper Flash just that little bit less cumbersome:

#!/bin/bash
VERSIONS=$(sudo update-pepperflashplugin-nonfree --status)

UPGRADE=$(echo "$VERSIONS" |grep -oE '[^ ]+$' |uniq |wc -l)
UPGRADE=$(($UPGRADE - 1))

if [ $UPGRADE -ne 0 ]
then
    sudo update-pepperflashplugin-nonfree --install
fi

echo "$VERSIONS"

Check your Flash version

In general, this can be done on Adobe's site.

The full story

Here is the full story nicely written up.