You need to load it first.

app.loadJQueryUI(function () {
  $( "#accordion" ).accordion();
});

The code @yariplus posted will get rid of the warning. If you somehow have 2 different plugins listening to the same widget hook you should set the html object on the data itself like so.

// filter:widget.render:widget
exports.renderWidget = function (data, next) {
   data.html = "<b>Awesome Widget</b>";
   next(null, data);
}

Take a look at https://github.com/NodeBB/nodebb-plugin-write-api

I just tested on this forum and it seems to work fine. What version are you on?

What would you put after the &? The post id? So &61013 would link to https://community.nodebb.org/post/61013?

You might have some other css that is overriding it with !important. Inspect the navbar in your browser and check it's css.

.navbar { 
    background-color: red;
}

Doesn't work?

Here is what you need to do in your plugin.

myPlugin.renderWidget = function (data, callback) {
  //render html
  var html = render();
  data.html = html;
  callback(null, data);
};

That will get rid of the warning.

I believe this broke when the cropper module was added. It shows the animated gif while cropping but when you save the image is turned into a png

I don't think it is possible right now since they both use the same method and hook, are you trying to change post content only in a topic? You might be able to use another hook that is only called when inside a topic.