All of a sudden, new tabs have started opening up (in Firefox) advertising games and other stuff. Any idea's of what is going on here?

Try scanning for malware using the removal tools listed near the bottom of the [[Troubleshoot Firefox issues caused by malware]] article. It might also help if you could copy and paste troubleshooting information into your reply. See [[Use the Troubleshooting Information page to help fix Firefox issues]] for details.