Currently, when I copy-paste (between Firefox, LibreOffice, etc), formatting like font, font size and font attributes get also copied and pasted. But I am looking for a way to copy-paste such that the format of the original text is discarded and instead the format of the target document is used, as if I had typed the text on the keyboard.

  (My wife uses the following trick on Windows: copy-paste text into URL-field of the browser, then copy-paste from URL-field to destination).