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I see Notifications Preferences and the only such preferences offered are Receive Alerts|Mute all notifications, Receive @all and @here mentions|Mute@all and @here mentions, and Show counter|Hide counter. Below is a screenshot of all my Notifications Preferences using Firefox 56 on a Windows laptop, ditto for IE 11. Did your chat implementation team test those platforms? I don't want to have to keep chat open all the time to know about new messages. Before the recent changes I had been relying on email forwarding of new chat messages and that worked well before June 17 2018. I do not need or expect to use any of the new chat features recently introduced.

Trying with Internet Explorer 11 gives the same results as with Firefox - int chat no options for Email or Mobile In Notifications Preferences and no Notifications section

With Firefox on a Windows laptop  there are no options for Email or Mobile In Notifications Preferences and there is no Notifications section.  Before 6/17/2018 there was an Email option in Notifications Preferences that I configured to forward all chat messages to email and had been working fine for the last few months.

I found it, thanks!  On my browser the minimize button shows up as W for "wide" I guess, and hovering on it pops up no clue as with the other buttons below it. On the minimized chat frame there is an S button, for "small" I guess, and clicking on it maximizes chat.

What minimize button? I don't see one using firefox on a laptop. What I have done so far that worked is to  use the "Remove it Permanently" firefox add-on to completely remove the chat frame and that has to be done for each window. I would rather not have chat come up automatically, but have a way to open it on demand. I have all chat sent to email and mostly just read them with Gmail.