fix for when trying to start firefox with a backed up profile and already existing extension.

Fixes Issue #8521

Signed-off-by: Luke Inman-Semerau <[email protected]>

Author: calinmarina

py/selenium/webdriver/firefox/firefox_profile.py

@@ -278,7 +278,8 @@ def _install_extension(self, addon, unpack=True):
                 os.makedirs(extensions_path)
             shutil.copy(xpifile, addon_path + '.xpi')
         else:
-            shutil.copytree(addon, addon_path, symlinks=True)
+            if not os.path.exists(addon_path):
+                shutil.copytree(addon, addon_path, symlinks=True)
 
         # remove the temporary directory, if any
         if tmpdir: