I have purged cookies but the problem persists. 
The Debug msg. in the browser window states:
 	
	| DBG 4.6.3 
 Failed to start DBG session
 
 Reason: failed to connect to the client at 127.0.0.1:7869, please make sure that IDE is running
 Not sure what it means? Visit http://www.nusphere.com/dbg/ for troubleshooting.
 
 Debugger request:   "412115926759000003;d=1,p=0,c=1"
 Request found in:   "$_COOKIE['DBGSESSID']"
 Target PHP version: "5.3.x"
 Server API:         "Apache 2.0 Handler"
 Extensions API:     "220090626"
 Modules API:        "20090626"
 PHP API:            "20090626"
 | 
Here is how to reproduce the problem:
– Create PhpED project using a vHost on a local WAMP installation.
– In PhpED select:  Tools-->Default Browser-->Google Chrome
– Run project in Debugger (F9). Chrome window opens.
– Terminate PhpED and close the Chrome debugging window.
– Try to open the URL of the vHost in a new Chrome window. This either leads to the above error message or to an unwanted start of PhpED.
– If you select another default browser in PhpED, the problem does NOT go away. So the vHost is not usable from within Chrome anymore (only if PhpED is running in background).
– Workaround to get Chrome working again:  Run project in PhpED without debugger (Ctrl+F9). Then close PhpED.
It looks like PhpED leaves some breakpoints within the PHP code after a Debugging session, even if PhpED is terminated. 
Only by running once without debugger (Ctrl+F9) this breakpoint info can be purged. I should also be purged whenever PhpED is terminated!
Without knowing the Ctrl-F9 workaround the vHost becomes completely unusable outside of PhpED.