The attempt to paste text shows absolutely nothing. I can paste formatted text into other non-XF forums, WordPress, etc. — exactly as before.
With a late beta of iOS 10 on my iPhone 6, plain text works, formatted text appears and promptly vanishes from the message window.
If the text is unformatted, no problem whatever. Firefox doesn't appear to support putting formatted text into a forum message window.
I have tested this problem in this forum, and on the three XF forums on my sites. Same symptoms. I also notice that putting in a full URL in my forum no longer displays the title attribute as it used to.
You can see the formatted text displayed in a forum window on one of my forums that was posted before your last update: