How to disable caret blinking in textboxes in Firefox?
The only idea related to that I found was to set ui.caretblinktime to 0, but that setting doesn't exist anymore.
You have to create the config key yourself.
Visit about:config, then enter ui.caretBlinkTime into the config search bar, add it (plus symbol button) as a Number type and set the value to zero.
Worked for me on Firefox 76.
Source: https://www.reddit.com/r/MacOS/comments/cnt7qp/how_to_adjust_cursor_blink_rate_in_webkit_not/ewe53db/