overload log_path to accept tuple (path, mode)

This change allows users to specify how they want
to open their log file with a fallback to `a+`
if nothing else is specified

Fixes SeleniumHQ#10703

py/selenium/webdriver/firefox/service.py

@@ -15,7 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 
-from typing import List
+from typing import List, Tuple
 
 from selenium.webdriver.common import (service, utils)
 
@@ -28,7 +28,7 @@ class Service(service.Service):
 
     def __init__(self, executable_path: str = DEFAULT_EXECUTABLE_PATH,
                  port: int = 0, service_args: List[str] = None,
-                 log_path: str = "geckodriver.log", env: dict = None):
+                 log_path: Union[str, Tuple[str, str]] = "geckodriver.log", env: dict = None):
         """Creates a new instance of the GeckoDriver remote service proxy.
 
         GeckoDriver provides a HTTP interface speaking the W3C WebDriver
@@ -41,12 +41,14 @@ def __init__(self, executable_path: str = DEFAULT_EXECUTABLE_PATH,
         :param service_args: Optional list of arguments to pass to the
             GeckoDriver binary.
         :param log_path: Optional path for the GeckoDriver to log to.
-            Defaults to _geckodriver.log_ in the current working directory.
+            Can also be called with (path_name, mode).
+            Defaults to _geckodriver.log_ in the current working directory and _a+_ respectively.
         :param env: Optional dictionary of output variables to expose
             in the services' environment.
-
         """
-        log_file = open(log_path, "a+", encoding='utf-8') if log_path else None
+
+        log_path, log_path_mode = (log_path[0], log_path[1]) if isinstance(log_path,Tuple) else (log_path, "a+")
+        log_file = open(log_path, log_path_mode, encoding='utf-8') if log_path else None
 
         super().__init__(executable_path, port=port, log_file=log_file, env=env)
         self.service_args = service_args or []