Control-click on a Mac is similar to right-click on a Windows computer, and is how you open shortcut (or contextual) menus on a Mac.

 1. Control-click: Press and hold the Control key while you click an item.

   For example, Control-click an icon, a window, the toolbar, the desktop, or another item. The options shown in the shortcut menu vary depending on the item you click.

 2.  Customize how you Control-click: Change options for your trackpad or for your mouse.

To be clear the issues is with FF displaying the shortcut menu on a different monitor when the Mac has additional external monitors attached.

I am experiencing the same issue on my MacBook Pro Retina 13" running Catalina (10.5.2).

Same setup: external monitor, connected via Display Port; same issue: when the active Firefox window is on the second (external) display, contextual menus appear on the primary (internal) display. Because the resolutions are different between the two displays moreover, the context menu text is tiny. Also, Firefox does not remember its last display, so, when launched, it always opens its main window in the first display (monitor). Other apps, when last closed on the second display, open up in the second display when re-launched.

I'm having the same problem as @will5 and @fedec. When viewing Firefox on an external second screen to a MacBook Pro running Catalina OS, some tooltips appear back on the laptop screen. This didn't happen before updating to Catalina OS.

This issue started happening a couple months ago. I don't remember the exact date or if I had just updated to a new version of FF or installed a new Mac OS update.

From what I can tell, when I right-click on my external monitor, the context menu displays in just about the same position, but on the primary monitor.

I've tried FF 75.0 and FF 76 betas (the latest being beta 4).

Unfortunately, I've had to switch to a different browser until this issue is resolved. :'( Hopefully the issue can be tracked down and fixed.

My current machine is an iMac:

MacOS 10.15.4

Monitor Retina 5k, 27-inch, 2019 Processor 3.6 Ghz i9 Memory 40g Graphics Radeon Pro Vega 8GB

My second monitor is BenQ 27 inch 4K PhotoVue.

I have the BenQ to the right of the iMac.

If any more information is needed please reach out.

That is a known bug.

• Bug 1592416 - Right click opens context menu on wrong monitor or virtual desktop (mac OS Catalina)

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)