This indicates an attack attempt against a command execution vulnerability in DXStudio Firefox Plugin.
The vulnerability is caused by an error when the vulnerable software handles a malicious shell.execute script. It allows a remote attacker to execute arbitrary command via sending a crafted web page.
Worldweaver DX Studio Player 184.108.40.206, 220.127.116.11, 18.104.22.168, and probably other versions before 22.214.171.124
Upgrade to DX Studio Player version v126.96.36.199 or later.