These instructions are relevant to current Moodle (3.4)
How to cut and paste text from Word retaining the formatting. How to use keyboard shortcuts to copy and paste in Firefox.
The menu on the right hand mouse button for Copy, Cut and Paste don't work in Firefox, so you need to use keyboard shortcuts.
The Atto Editor has a "smart paste" feature which will strip out incompatible formatting codes, so simply copy from your Word or other document and paste into Moodle using the right mouse button menu.
If you need to simplify the formatting, select the text you need to simplify and click the Tx button.
It is always best to do as much formatting as possible in Moodle rather than beforehand in Word or other program.