Thread:Extension talk:TogetherJS/The logo of TogetherJS is not visible in editing toolbar.

File "ext.togetherjs.js"

line 30

Change

imageFile: '//pinklake.wmflabs.org/extensions/TogetherJS/togetherjs/images/togetherjs-logo.png',

to

imageFile: '//raw.github.com/ianb/togetherjs/master/site/images/togetherjs-logo.png',

or just copy the image into your Mediawiki folder and change the path accordingly.