diff --git a/betty/app/__init__.py b/betty/app/__init__.py
index 69836580e..fc8d55224 100644
--- a/betty/app/__init__.py
+++ b/betty/app/__init__.py
@@ -12,8 +12,6 @@
 from babel.core import parse_locale
 from babel.localedata import locale_identifiers
 
-from betty.resource import Releaser, Acquirer
-
 try:
     from typing import Self  # type: ignore
 except ImportError:
@@ -116,7 +114,7 @@ def dump(self) -> DumpedConfiguration:
 
 
 @reactive
-class App(Acquirer, Releaser, Configurable[AppConfiguration], ReactiveInstance):
+class App(Configurable[AppConfiguration], ReactiveInstance):
     def __init__(self, *args, **kwargs):
         from betty.url import AppUrlGenerator, StaticPathUrlGenerator
 
@@ -167,12 +165,6 @@ def acquire(self) -> None:
             self._acquire_contexts.enter_context(Translations(NullTranslations()))
             # Then acquire the actual locale.
             self._acquire_contexts.enter_context(self.acquire_locale())
-
-            for extension in self.extensions.flatten():
-                if isinstance(extension, Acquirer):
-                    extension.acquire()
-                if isinstance(extension, Releaser):
-                    self._acquire_contexts.callback(extension.release)
         except BaseException:
             self.release()
             raise
diff --git a/betty/gui/error.py b/betty/gui/error.py
index ffe0410f5..2a8a862c1 100644
--- a/betty/gui/error.py
+++ b/betty/gui/error.py
@@ -2,7 +2,7 @@
 
 import functools
 import traceback
-from typing import Optional, Callable, Any, List, TYPE_CHECKING
+from typing import Optional, Callable, Any, TYPE_CHECKING
 
 if TYPE_CHECKING:
     from betty.builtins import _
@@ -69,8 +69,6 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 
 
 class Error(QMessageBox):
-    _errors: List[Error] = []
-
     def __init__(
             self,
             message: str,
@@ -83,7 +81,6 @@ def __init__(
         with App():
             self.setWindowTitle('{error} - Betty'.format(error=_("Error")))
         self.setText(message)
-        Error._errors.append(self)
 
         standard_button = QMessageBox.StandardButton.Close
         self.setStandardButtons(standard_button)
@@ -93,7 +90,6 @@ def __init__(
         self.button(QMessageBox.StandardButton.Close).clicked.connect(self.close)  # type: ignore
 
     def closeEvent(self, event: QCloseEvent) -> None:
-        Error._errors.remove(self)
         if self._close_parent:
             parent = self.parent()
             if isinstance(parent, QWidget):
diff --git a/betty/resource.py b/betty/resource.py
deleted file mode 100644
index 19b5b900f..000000000
--- a/betty/resource.py
+++ /dev/null
@@ -1,8 +0,0 @@
-class Acquirer:
-    def acquire(self) -> None:
-        raise NotImplementedError
-
-
-class Releaser:
-    def release(self) -> None:
-        raise NotImplementedError