I'm trying to play a game on 360Game but I am getting the following error:
Context3D not available! Possible reasons: wrong wmode or missing device support.
What could be the issue? How can I fix it? I am using Firefox 68.0 on Ubuntu 16.04.6
That's more of a browser question than an Ubuntu question.
I would suggest trying some other browsers first, such as Brave being my favorite, Chromium, etc... See if that makes a difference.
The game may need the Flash plugin, which is deprecated and the world is moving away from it, but it can still be done if absolutely needed.
The game may be a Microsoft Active-X game - which based on the error may be likely - in which case there may not be a reasonable fix.
The game may be a Java game, try making sure you have the Java plugin installed.
Research shows (thank you, Kulfy!) this is a Flash based issue, and the website developer uses tools which don't work well with 64-bit Firefox. However, since Firefox is Open Source, other developers have a spin-off Firefox based browser which is 32-bit, for Ubuntu 16.04.
It's called Pale Moon and you can download the installation files. Once downloaded, do
sudo dpkg -i palemoon_126.96.36.199+repack-1_i386.deb to install Pale Moon. Once you start Pale Moon, you will see it's Firefox with some different colors, and will take nearly all the Firefox plugins and extensions (excepting, of course, 64-bit add-ons).