I'm using Microsoft Outlook 365 in a Firefox browser tab. While composing an email, I cannot right click and paste into the email draft.
Please don't ask me to clear cookies and cache. That has been a painful experience.
What happens when you try to right-click > Paste? Is there an error message? Layout is wrecked? Something else?
If the site substitutes its own menu for Firefox's context menu, hold down the Shift key when right-clicking to get Firefox's menu.