Theme Switcher in 3.3.x

When i switch the theme by new outfit. Is ok.
But when i close my browser or test from another pc and start, the theme ist old default.

The problem is probably on the browser!
No problem with InternetExplorer!
With Firefox always starts the old classical theme.
When switching it is ok, until the firefox is restarted

Any ideas?

Old theme defaults when you clear your browser cache.