I think this issue might be a little niche, but it’s something I’ve been experiencing for at least a week, first I thought it was just my forum, but I just happened to see it on Meta.
I’m running Firefox 60.6.2esr on Debian 9.
The issue is that every time I try to write a message in Discourse the pointer thingy doesn’t appears (the texts gets written), so I don’t get text correction, nor the ability to add Latin characters. Just clicking away anywhere and then clicking back to continue writing fixes the issue.
As soon as the text pointer appears, the text input normalizes.