I use the right click context menu a LOT, and it's really annoying when I click an item inside this menu by accident with the right mouse button and activate that item.
If I bring up a right-click context menu, I want an option to make it so that I can only activate items inside this menu with the left mouse button.
I brought this idea up on the Firefox subreddit, and it got some attention, but it sounds like the only way to change this behavior would be to change how Firefox handles mouse events in its source code.
For people who are prone to accidentally clicking things or making involuntary movements, I think this would be a great accessibility feature.