I don’t have a preview pane any more. Did something break on the website or is it my problem only?
There is a little icon that looks like >> below the lower right corner of the post entry box. Click that to restore the preview pane. Once the preview pane is visible you’ll notice another icon below the lower right corner of the preview pane that looks like <<. Click that to make the preview pane disappear again.
Both are easy to click by accident, especially on a touch screen.
Those buttons are still there, but when I click the one with mouse-over “show preview”, space for the preview pane appears, but it’s empty.
Huh. I never knew what the icon was for (it looks a little TV on the mobile app on my phone). It also shows my text when I click on it. Looks like the Lawrence Welk video I plan to show Mr. Legend when he gets up also shows as a link, although nothing happens when I click on it on the preview.
Preview works on my phone, with a screen button.
Preview also works on my computer when I highlight text and choose Quote.
And any other use of Quote activates the preview pane.
There must be something weird going on with style sheet I’m using, which seems to be Straight Dope Light.
I’m on straight dope light. Using Edge on Windows 10. I’ve had no issues.
At this point all I can suggest is clear the cached data for this site, fully close and reopen all instances of your browser, and if that doesn’t work try a reboot.
You definitely have something weird going on local to your machine. Did you by any chance recently change anything about any ad blockers you may have? That can foul up various scripts.
Yep, done all that.
It’s quite possible the corporate firewall is mucking things up. I’m not expecting much of a resolution, mostly just documenting it cause that’s what I do. 
Are you using an ad blocker? Depending on which one you use, it can be very easy to mistakenly add a page element to your ad blocker’s naughty list.
Not on that computer, except for the firewall. The 1Blocker app on my phone gives no trouble, but this site seems to behave differently on phone vs computer. I’ll try at my home computer sometime.