Double Klick fails to open new tab

After updating to Yosemite double klick does not open a new TAB anymore??
I found a post that pressing cmd would help. But this fails still on my mac… i tried many combinations… to no avail. I find a post that this should be solved by 1.6.16
Am I doing something completely wrong? I reinstalled 1.6.17… still double klick on the folder icon of the desctop does not open a new tab…
Any proposal?