There is a simple keyboard shortcut, if you have copied formatted text and want to paste it into the फ़ायरफ़ॉक्स browser as unformatted text.
To paste the text as unformatted plain text into फ़ायरफ़ॉक्स browser, press the following keys:
क्या Ctrl + पाली + V
No extra plugins are required. This was tested in Firefox 52 on विंडोज़ 10. If this works in a different Firefox version or does not work in a specific Firefox version on various platforms let us and other users know in the comments section below.