log initialization errors in the background page

extension/core/scripts/content/content.js

@@ -48,7 +48,7 @@
 					processing = false;
 				})
 				.catch(error => {
-					browser.runtime.sendMessage({ processError: true });
+					browser.runtime.sendMessage({ processError: true, error });
 					processing = false;
 					throw error;
 				});

extension/ui/scripts/bg/ui.js

@@ -71,6 +71,9 @@ singlefile.ui = (() => {
 			onTabEnd(sender.tab.id);
 		}
 		if (request.processError) {
+			if (request.error) {
+				console.error("Initialization error", request.error); // eslint-disable-line no-console
+			}
 			onTabError(sender.tab.id);
 		}
 		return false;