tty.js/static/user.js to enable context-menu pasting in Firefox/gecko with tty.js web terminal.

user.js

var on = window.Terminal.on;
var isGecko = navigator.userAgent.indexOf('WebKit')==-1 && navigator.product == 'Gecko';
var isChromium = window.chrome;

// replace bindPaste with a variant that:
// 1. doesn't set contentEditable back to 'inherit'
// 2. replaces newlines with carriage returns in the clip
// 3. moves the caret (i.e. the contentEditable cursor) out of sight.

window.Terminal.bindPaste = function(document) {
  // This seems to work well for ctrl-V and middle-click,
  // even without the contentEditable workaround.
  var window = document.defaultView;
  on(window, 'paste', function(ev) {
    //console.log('paste handler called');
    var term = Terminal.focus;
    if (!term) return;
    var clip;  
    if (ev.clipboardData) {
      clip = ev.clipboardData.getData('text/plain');
    } else if (term.context.clipboardData) {
      clip = term.context.clipboardData.getData('Text');
    }
    // Its a safe bet that newlines in the clipboard should be sent as ^m  
    clip = clip.replace(/\n/g, "\r");
    term.send(clip);
    // consider redraw the terminal since the pasted text may be cluttering it up.
//    term.refresh(0, term.rows - 1);
    placeCaretAtEnd( term.element );
//    If we do this, we can't paste any more...
//    term.element.contentEditable = 'inherit';
    term.cancel(ev);  
  });
};

// patchup Terminal.open to add a new mousedown handler that pretty aggressively 
// sets contentEditable to true.  Also disables spellcheck (HTML5 browsers).
var oldopen = window.Terminal.prototype.open;
window.Terminal.prototype.open = function (parent) {
    var self = this;
    oldopen.apply(this, arguments);

  if (isGecko || isChromium) {
      on(this.element, 'mousedown', function(ev) {
          console.log('new mousedown code reached');
          var button = ev.button != null
              ? +ev.button
              : ev.which != null
              ? ev.which - 1
              : null;
          if (button !== 2) return;
          //      ev.target.addEventListener('DOMCharacterDataModified', _handler, false);
          ev.target.contentEditable = true;
      }, true);

      self.element.contentEditable = true;
  }
  self.element.spellcheck = false;
};

function placeCaretAtEnd(el) {
    el.focus();
    if (typeof window.getSelection != "undefined"
            && typeof document.createRange != "undefined") {
        var range = document.createRange();
        range.selectNodeContents(el);
        range.collapse(false);
        var sel = window.getSelection();
        sel.removeAllRanges();
        sel.addRange(range);
    } else if (typeof document.body.createTextRange != "undefined") {
        var textRange = document.body.createTextRange();
        textRange.moveToElementText(el);
        textRange.collapse(false);
        textRange.select();
    }
}