Comment 1 for bug 977981

diff --git a/extensions/adblock.c b/extensions/adblock.c
index 0d46d9e..9ba8095 100644
--- a/extensions/adblock.c
+++ b/extensions/adblock.c
@@ -840,6 +840,7 @@ adblock_custom_block_image_cb (GtkWidget* widget,
     GtkWidget* entry;
     gchar* title;

+ g_return_if_fail (MIDORI_IS_EXTENSION (extension));
     app = midori_extension_get_app (extension);
     browser = katze_object_get_object (app, "browser");

Can you please try this workaround?

callback of midori_browser_foreach () have only 2 arguments, while we expecting 3. which is causing MidoriExtension which we are passing to be null.