Try updating to the most recent Firefox (Firefox 10.0.2) Firefox 3.6 is going to be dropped from support in April and will no longer receive any updates.

After installing Firefox 10, try again. If it still doesn't work, try downloading http://fpdownload.macromedia.com/pub/flashplayer/current/licensing/win/install_flash_player_11_plugin_32bit.exe.

Thanx Tyler for your quick reply. Following you advice, and keeping my current Firefox version, I played arround with the 32-bit and 64-bit versions of Shockwave Flash. There doesn't seem to be any difference between the two. The issue remains for those two websites listed in my post above. Other websites with embedded vids work fine with the Shockwave Flash add-on. And till yesterday those other two sites wefre working fine, too. I do not want to install the newest version of FF yet ( and mine is currently still supported). Any other suggestion as to why those 2 sites ask me to open the embedded vids with the VLC program instead or running the videos within FF? Thank you for any advice on this.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

thanks cor-el. Issue was partially solved by upgrading to latest FF version. This link - however - is still not working. The slide show doesnt work: http://www.spineuniverse.com/conditions/back-pain/slideshow-how-keep-healthy-spine?page=2#top ..but I can live with this (-: