Code to open web browser crashes ArcMap when run from a Python add-in

I created an ArcMap Python add-in using ArcGIS 10.1 to open a webpage after the map is clicked. It opens the page but then ArcGIS crashes.

import arcpy
import pythonaddins
import webbrowser

class ToolClass2(object):
    """Implementation for TEST_addin.tool (Tool)"""
    def __init__(self):
        self.enabled = True
        self.cursor=3
    def onMouseDownMap(self, x, y, button, shift):

    mxd=arcpy.mapping.MapDocument("current")
    df = arcpy.mapping.ListDataFrames(mxd)[0]
    pt=arcpy.PointGeometry(arcpy.Point(x,y))

    pythonaddins.MessageBox("Long" + " " + str(x) + '\n'+ "Lat"+ " " + str(y), 'Coordinates', 0)
    path = 'http://pol.pictometry.com/en-us/php/default.php?lat=' +str(x) +'&lon=' + str(y)+'&v=p&o=n&type=or&level=n'
    webbrowser.open(path)
    pass