Flash Player linux, grey box issue (youtube vids and some applets do not display)

Question

I posted this question on my distro-specific forum as well as linuxquestions.org, 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?

Answer 1

The problem, at least in my case, was QtCurve's opacity. If I have opacity set to less than 100%, flash would not display for sites like Youtube and Vimeo, but worked elsewhere.
The solution for me was to go into qtcurve's settings, and put npviewer.bin in the application exceptions section for window and menu opacity. Doing that, I was able to keep my transparent menus, and also use flash everywhere.
You can find out what the application name is by launching your browser of choice in a terminal with qtcurve debug turned on, like so:
QTCURVE_DEBUG=1 firefox
If you watch through the lines that start with "QtCurve" you'll see "Application name". Look for the one that shows up when you try to load a video. In my case it was npviewer.bin. In yours, it might be nspluginviewer or something else. If you add an exception for that specific application, you'll fix your problem without having to compromise on your theme.