No line wrap?

[NCDiesel]

Just converted to SMF from vBulletin and liking it so far.  I am using the studio theme on my site (antique-tractor.com/forum) and have a problem with new posts and replies.   I am having complaints from Firefox and Edge users that the text box for new posts/replies (the main text box) that any line won't wrap  and the right edge is off the screen - it just goes on forever.   It will display correctly after they post but unless they manually break the line it won't line wrap.  Line wrap works fine with Chrome;  but I was able to replicate it with Firefox.   Works fine on mobile devices too.

I am a CSS neophyte and don't even know where to start looking.  Any ideas where in the CSS and/or theme template I need to look to find culprits?

PS:  SMF 2.0.15

[Pipke]

Think you should get better support by the theme author, wich is on this case at http://webtiryaki.com/