Localization of the context menu

[YD-89]

Before submitting a bug report

• I updated to the latest version of Multi-Account Container and tested if I can reproduce the issue
• I searched for existing reports to see if it hasn't already been reported

Step to reproduce

On any web page, in a loalized version of Firefox, right click on a link. In the submenu of MAC, all items are in english. My locale is french, the addon is 100% translated in Pontoon for that locale.

Actual behavior

Right-clicking a link on a web page displays options of MAC in english instead of the locale of Firefox.

Expected behavior

They should be translated.

Additional informations

The untranslated items are not in the MAC strings of Pontoon.

Provide a copy of Troubleshooting Information page (optional)

No response