At least 3 reports on #wikimedia-tech that they're unable to save edits, view previews or diffs.
Two reports of FF 69 on 18.04 and Windows 10. One report of IE 11
Not much more information atm...
[16:37:16] <ahecht> Anyone else having trouble creating pages on enwiki? I can browse fine, but when I hit publish i just get a very long wait followed by my browser timing out.