Very useful but has some issues worth mentioning. Seems to conflict with 7tv (tbf it's hard not to), @ mentions revert the chat box to (expanded) horizontal. Recently, I've had an issue where the chat box has to be expanded before the switch to vertical mode, otherwise it causes severe visual bugs. As far as I can tell, the mode toggle auto-collapses the chat box, so hitting it 4 times might be enough to reproduce this issue (pretty common issue with the 7tv issue). Hope that's helpful.

I like to put streams i watch on my vertical monitor, and this extension works flawlessly on Chrome.
Using this extension on Firefox causes the vertical mode to exit to default by itself if i click out of the window and clicking back into it. It's quite annoying because i nee to enter vertical mode each time i want to write to the streamer.
I'll give this extension 5 stars if this bug can be fixed.