When I start a reply in the Waterfox browser even on this forum, the cursor does not appear when typing, making it difficult to reposition the cursor to edit text:
The cursor displays fine when I start a new topic or private message, but does not appear when I reply to an existing topic or private message.
This issue does not occur on Chrome or Edge. On the Discourse based forum I take care of, someone mentioned the cursor does not appear on their Firefox browser when replying, although the cursor appears for me in Firefox.
To replicate this issue, try to reply to any topic here in the Waterfox 64-bit browser, such as the portable version which is also affected.
From checking that BugZilla thread, this issue affects Firefox ESR, the extended support release for organisations. The example David points to is another Discourse based forum.
To test, I installed Firefox ESR (60.7.1esr 64-bit) and as I write this reply the cursor is missing. The workaround they mention (minimise and restore) does indeed trigger the cursor to appear.
I will reply to that BugZilla thread to mention this.