KDE 4.2, ext. soundcard, firefox - flash playback problem


Would someone have an idea what to do here?

Here’s what I have:

OpenSUSE 11.1 with KDE 4.2
Firefox 3.0.11
flashplayer installed and enabled (as is Java, in case that makes a difference)
External USB sound card: Creative SB Live! 24bit

In Yast2 > Hardware > Sound, the external card is configured as USB audio and set as primary sound card

In Personal Settings > Multimedia, the external card is set as first preference for all audio playback.

The system recognizes the external sound card and switches to it, but despite this it works only very patchily with all flash video content on Firefox (youtube, other places). Sometimes it works after repeated disconnecting and reconnecting, switching off and switching on, reconfiguring, reloading Firefox. Now this refused to have any effect. There’s no problem with playback of audio or video files on the computer.

Am I missing something in the configuration, or is the conclusion that it’s the flash plugin and there’s nothing to be done? Thanks.