Also, lots of our members complain they cannot access half the pages in the topmenu. For instance, the 'IRC CHAT' link is inaccessable for éveryone but me. Even for all the other administrators.
Your IRC iframe looks ok to me, unless you mean the IRC login is failing. If so, the issue is with the page loading in the iframe:
Your TS3 iframe from gametracker is showing correctly for me also so it doesn't appear to be an issue with your site configuration. Ask your members to ensure the correct settings are enabled in their chosen browser.
As rod mentions please provide details regarding your server and xoops environment. This is key to troubleshooting your issues.
Post your specific issues separately and clearly, folks are more apt to respond to 'Iframe issue' than '(read before rage)'