Firefox Key Equivalent Fixer

main.m

#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>
#import "ZKSwizzle.h"




@interface myNSApplication : NSApplication
@end


@implementation myNSApplication

- (void)sendEvent:(NSEvent *)event {
	// Firefox does not handle user-defined key equivalents properly
	// https://bugzilla.mozilla.org/show_bug.cgi?id=1333781
	
	// Check if the event is a key down event with a modifier key. (Otherwise, it can't be a keyboard shortcut.)
	if (
		[event type] == NSKeyDown &&
		[event modifierFlags] & (NSCommandKeyMask | NSAlternateKeyMask | NSControlKeyMask)
		//We don't check NSShiftKeyMask because shortcuts aren't allowed to use Shift as the only modifier key.
	) {		
		// Query user-defined key equivalents
		NSDictionary *userKeyEquivalents = [[NSUserDefaults standardUserDefaults] objectForKey:@"NSUserKeyEquivalents"];

		if (userKeyEquivalents) {
			// Check if the event matches any user-defined key equivalents
			for (NSString *menuItemTitle in userKeyEquivalents) {
				NSString *shortcut = userKeyEquivalents[menuItemTitle];
				if ([self event:event matchesShortcut:shortcut]) {
					[self performKeyEquivalent:event];
					[self performActionForItemWithTitle:menuItemTitle inMenu:[NSApp mainMenu]];
					return;
				}
			}
		}
	}
	// Pass event to Firefox to handle normally.
	ZKOrig(void, event);
}



- (BOOL)event:(NSEvent *)event matchesShortcut:(NSString *)shortcut {
	// Convert the shortcut string to a key equivalent and modifier mask
	NSString *characterKey = [shortcut substringFromIndex:[shortcut length] - 1];
	NSString *modifierString = [shortcut substringToIndex:[shortcut length] - 1];
	NSUInteger modifierMask = 0;
	for (int i = 0; i < [modifierString length]; i++) {
		switch ([modifierString characterAtIndex:i]) {
			case '@':
				modifierMask |= NSCommandKeyMask;
				break;
			case '~':
				modifierMask |= NSAlternateKeyMask;
				break;
			case '^':
				modifierMask |= NSControlKeyMask;
				break;
			case '$':
				modifierMask |= NSShiftKeyMask;
				break;
		}
	}
	// Compare with the event
	return (
		[[[event charactersIgnoringModifiers] lowercaseString] isEqualToString:characterKey] &&
		([event modifierFlags] & NSDeviceIndependentModifierFlagsMask) == modifierMask
	);
}

- (void)performActionForItemWithTitle:(NSString *)title inMenu:(NSMenu *)menu {	
	for (NSMenuItem *menuItem in [menu itemArray]) {
		if ([menuItem hasSubmenu]) {
			[self performActionForItemWithTitle:title inMenu:[menuItem submenu]];
		} else {
			
			//Ensure three periods ("...") matches the elipses character ("…").
			title = [title stringByReplacingOccurrencesOfString:@"..." withString:@"…"];
			NSString *menuItemTitle = [[menuItem title] stringByReplacingOccurrencesOfString:@"..." withString:@"…"];
			
			if ([menuItemTitle isEqualToString:title]) {
				[[menuItem menu] update]; //highlight menu
				[[menuItem menu] performActionForItemAtIndex:[[menuItem menu] indexOfItem:menuItem]];
				return;
			}
		}
	}
}

@end




@interface myNSWindow : NSWindow
@end


@implementation myNSWindow

- (BOOL)makeFirstResponder:(NSResponder *)responder {
				
	//Initialize menus to ensure:
	//1. Every item can be triggerred by its key equivalents
	//2. Every item can appear in the search results of the `Help` search box.
	[self initializeSubmenusOf: [NSApp mainMenu]];
	
	//We should also listen for menu changes. Unfortunately, the below code will crash Firefox.
	//Todo: figure out how to do this properly!
	/*[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(initializeSubmenusOf:) name:@"NSMenuDidAddItemNotification" object:[NSApp mainMenu]];
	[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(initializeSubmenusOf:) name:@"NSMenuDidRemoveItemNotification" object:[NSApp mainMenu]];*/
	
	return ZKOrig(BOOL, responder);
}

- (void)initializeSubmenusOf:(NSMenu *)menu {
	[[menu delegate] performSelector:@selector(menuWillOpen:) withObject:menu];
	[[menu delegate] performSelector:@selector(menuDidClose:) withObject:menu];

	for (NSMenuItem *menuItem in [menu itemArray]) {
		if ([menuItem hasSubmenu]) {
			[self initializeSubmenusOf:[menuItem submenu]];
		}
		
		[self fixUpMenuItem: menuItem];
	}
}

- (void)fixUpMenuItem:(NSMenuItem *)menuItem {	
	// In Firefox, `Select All` menu item is initially disabled for some reason
	if (![menuItem isEnabled] && [[menuItem title] isEqualToString:NSLocalizedString(@"Select All", nil)]) {
		[menuItem setEnabled:YES];
	}
}

@end




@implementation NSObject (main)

+ (void)load {
	ZKSwizzle(myNSApplication, NSApplication);
	ZKSwizzle(myNSWindow, NSWindow);
}




@end


int main() {}

@isolinear I can use DYLD_INSERT_LIBRARIES, but I'm on a truly ancient version of macOS (10.9). I think on 10.15 you should be able to use DYLD_INSERT_LIBRARIES if you disable System Integrity Protection, is that turned on? If you want SIP, I think you could also use insert_dylib to add the library to the Firefox binary; you may need to re-sign Firefox afterwards. However, I'm unfortunately not familiar with modern macOS anymore, I know Apple has added tons of restrictions on code injection and it's one of the reasons I'm on this ancient version.