Shortcuts not working on Safari and Firefox

I just upgraded to Yosemite and have the following problem: no shortcuts for menu commands work anymore on Safari or Firefox. Simple test: start Safari and click cmd-Q to quit. Normally it should just quit. on my Macbook it doesn't. On Firefox, the menu bar flashes once, but that's about it.

A few facts:

• Macbook Pro (Retina, 15-inch, Early 2013)
• Mac OS 10.10 installed and running
• Both, Safari and Firefox, are upgraded to the latest versions.
• No keyboard additions installed
• Swiss keyboard installed
• Nothing changed regarding keyboard preferences

Anybody else experiencing the same or has any idea, how to fix it?

TIA