Issue #2666: Handle BROWSER environment variable properly for unknown browser…

Issue #2666: Handle BROWSER environment variable properly for unknown browser names in the webbrowser module.

Lib/webbrowser.py

@@ -625,7 +625,9 @@ if "BROWSER" in os.environ:
     # and prepend to _tryorder
     for cmdline in _userchoices:
         if cmdline != '':
-            _synthesize(cmdline, -1)
+            cmd = _synthesize(cmdline, -1)
+            if cmd[1] is None:
+                register(cmdline, None, GenericBrowser(cmdline), -1)
     cmdline = None # to make del work if _userchoices was empty
     del cmdline
     del _userchoices

Misc/NEWS

@@ -364,6 +364,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #2666: Handle BROWSER environment variable properly for unknown browser
+  names in the webbrowser module.
+
 - Issue #6054: Do not normalize stored pathnames in tarfile.
 
 - Issue #6794: Fix Decimal.compare_total and Decimal.compare_total_mag: NaN