I posted this question on my disto-specific forum, however it appears to be a unique problem, so here it is:

When viewing videos on youtube.com, most other websites, and when trying to run certain flash games, the flash applet will not display (though the audio will play). Instead of displaying the flash applet, there will be a grey box where the flash video or applet would normally be.

This problem occurs on Firefox and Chromium, but not on Opera.

My Specs are as follows:
Distro: PCLinuxOS 2010 (32-bit)
flash-player-plugin: 10.1-2pclos2010
firefox: 3.6.6-1pclos2010
swfdec has never been installed (to my knowledge)

I did a lot of investigating about the problem but have turned up no solutions thus far. Here are my results.

• Flash videos and applets which allow access to the settings menu (like youtube played from their website) do not display, however flash videos and applets which do NOT allow access to the settings menu (including youtube videos embedded in other websites) WILL display.
  
• Reinstalling flash-player-plugin and firefox through synaptic does not solve the problem (though note that PCLOS works with rpm files, not deb files. apt4rpm does not support the remove --purge operation, however reinstalls are said to overwrite custom configs with stock ones.)
  
• Creating a new firefox profile and/or starting FFox in safe-mode does not solve the problem
  
• Creating another user and running FFox from that user will properly display flash videos
  
• Comparing default plugins between my main user and new user shows that there is no difference. So this likely rules out a defective extension or plugin binary.
  
• Deleting ~/tmp/plugtmp* folders when FFox is closed does not solve the problem.
  
• Removing the ~/.macromedia and ~/.adobe folders does not solve the problem. (have checked permissions between the new test user and main user, and they are equivalent)
  
• Downloading libflashplayer.so from the Adobe website and copying it to /usr/lib/mozilla/plugins has no effect on the problem.

I'm thinking that there might be somewhere else that flash stores configurations for my user, and that maybe the settings there are corrupted and would need to be purged. However frantic googling has turned up nothing useful so far.

Does anyone have any suggestions for me?

One possibility is to remove Firefox, download it from Mozilla, and manually install it to /opt (Or run it from your home folder).
However, this will lose you any patches PCLOS has applied to it's Firefox package, which may include compatibility or fixes to make things work within PCLOS, and I can't be certain it will help.

My suggestion is to find the Better Privacy addon for Firefox, tell it to remove ALL flash cookies, and see if that has any effect.

Also, as apt4rpm does not support --purge, try asking it for a list of installed files the package gives (Can't remember if you can do this with APT, you may have to examine the source RPM to find all the files from the package), remove the package, then check to make sure all those files are deleted.

Finally, have a look at the LightSpark project - AFAIK it's an FLOSS implementation of Flash for Linux. I don't know what distributions it's packaged for, or if you'll have to compile it yourself, but it may solve the problem if it works.

Today I discovered that the problem occurs only when I'm logged into my user's KDE session. However when I'm logged into GNOME it works fine. I'd still like to get it working properly in KDE.

Perhaps what's needed is a clean-out of the ~/.kde (or /.kde4) directory? You might lose a few settings stored there, which is inconvenient, but if you make a note of the settings (so any issues caused don't just get copied back in again when you import them again) and re-set them all after the cleanout, that *should* fix it.
In theory.

1 members found this post helpful.

Thank you for your replies TheStarLion. Today I was experiencing problems with Openoffice crashing upon opening, while logged into KDE (but not GNOME) and have confirmed that both problems were caused by something in the .kde4 folder (more specifically ~/.kde4/share/config/) causing problems.

I have renamed the .kde4 folder and let KDE restore its settings from default, now both OOo and flash both work as intended. In other words your solution worked. Thanks again.

UPDATE: The exact file that was being changed improperly is the ~/.kde4/share/config/gtkrc-2.0 -- the exact cause of the bug is likely either the gtk-kde4 (allows one to configure GTK themes within the KDE CC) or qtcurve packages.

I have finally found the culprit, and it is a misconfiguration of QtCurve itself! The problem was solved by going into the QTCurve configurator and loading one of its presets. In finding this, I was able to completely restore-from-backup all of my old .kde4 settings minus the corrupted QTCurve settings.

Versions of related packages are:

gtk-kde4 0.9.4
kde4-style-qtcurve 1.5.1
qtcurve-gtk2 1.5.1