I don't know why typing particular words or characters would cause the page to scroll. Firefox has some "hotkeys" to open the Find bar or go to the end of the page, but navigation like that shouldn't affect what you had already typed in the form. Maybe there are some hotkeys defined by YouTube which could cause that?? Regarding pasting, an old issue from 2015 recently returned where YouTube throws away the pasted content in Firefox. If you only comment a few times a day, a workaround is to use a '''bookmarklet''' -- a script you save as a bookmark -- to bypass this problem. You can install it from here: https://www.jeffersonscher.com/res/sumomarklets.html#ytpaste If you use Greasemonkey, Tampermonkey, or Violentmonkey, there's a userscript version of this fix which can apply it automatically when you load a YouTube page: https://greasyfork.org/en/scripts/12433-fix-paste-on-youtube ---- Here's the technical explanation for what the bookmarklet script does (the userscript doesn't have the first two parts): <code>javascript: ...</code> => this protocol informs Firefox that the bookmark is actually a script <code>void( ... );</code> => this prevents Firefox from trying to load the script as a web address <code>addEventListener('paste', function(e){ ... }, true)</code> => this instructs Firefox to take action when you paste into the page ([https://developer.mozilla.org/docs/Web/API/EventTarget/addEventListener addEventListener on MDN]) <code>e.stopPropagation()</code> => this instructs Firefox not to pass the paste event to any other elements/scripts in the page, so Firefox just proceeds with pasting as normal ([https://developer.mozilla.org/docs/Web/API/Event/stopPropagation stopPropagation on MDN])

Try to disable accessibility services in Firefox. *Options/Preferences -> Privacy & Security -> Prevent accessibility services from accessing your browser *https://support.mozilla.org/en-US/kb/accessibility-services