The "null-V" keyboard shortcut is wrongly displayed on the "Shot Copied" notification, instead of "Ctrl-V" on Windows and "⌘-V" on Mac

[SoftVision-CosminMuntean]

[Affected versions]:

• Nightly 59.0a1
• Screenshots 24.0.0

[Affected Platforms]:

• All Windows
• All Mac OS
• All Linux

[Prerequisites]:

• The "xpinstall.signatures.required" boolean pref is set to "false".
• The "extensions.legacy.enabled" boolean pref is set tot "true".
• Have the Screenshots 24.0.0 dev version installed from here, on a new clean profile.

[Steps to reproduce]:

1. Open Firefox browser with the profile from prerequisites.
2. Navigate to any website and perform a selection.
3. Click the "Copy" button and observe the system notification.

[Expected result]:

• On Windows: The "Press Ctrl-V to paste" text is displayed.
• On Mac: The "Press ⌘-V to paste" text is displayed.

[Actual result]:

• The "Press null-V to paste" message is displayed on Windows and also on Mac.

[Notes]:

• Here is a screen shot with the issue:
  

[SoftVision-CosminMuntean]

I have verified that the issue is no longer reproducible using latest Screenshots dev version on Windows, Mac and Linux.