--- a/testing/mozbase/manifestparser/manifestparser/filters.py
+++ b/testing/mozbase/manifestparser/manifestparser/filters.py
@@ -351,17 +351,22 @@ class pathprefix(InstanceFilter):
         if isinstance(paths, basestring):
             paths = [paths]
         self.paths = paths
 
     def __call__(self, tests, values):
         for test in tests:
             for tp in self.paths:
                 tp = os.path.normpath(tp)
-                if not os.path.normpath(test['relpath']).startswith(tp):
+
+                path = test['relpath']
+                if os.path.isabs(tp):
+                    path = test['path']
+
+                if not os.path.normpath(path).startswith(tp):
                     continue
 
                 # any test path that points to a single file will be run no
                 # matter what, even if it's disabled
                 if 'disabled' in test and os.path.normpath(test['relpath']) == tp:
                     del test['disabled']
                 yield test
                 break