I found something for the selenium test but I dont see something for manually browsing. It looks like GMT is allways used.
I look for a way to test my local site with a specific timezone. Setting the timezone for the machine would also change the timezone for my local webserver (iis on windows) and thats not what I want.
I know I can set the time offset for firefox but this is also not my preferred way, because it realy sets an offset not a timezone with a different behaviour for daylight saving time.