I am having this wired issue which has taken me quite a while to pinpoint. In general my PS3 can see the Mediatomb running on my home server without problem. However the moment an Opera browser is running on any of my other computers, be it in the LAN or the bridged WLAN, the PS3 suddenly cannot find the Mediatomb anymore. Has anybody experienced any similar issues and found a fix or another workaround than simple closing opera?
I have found an improved workaround: disabling UPnP in Opera by turning of Opera Unite in opera:config. To do this visit opera:config, expand "User Prefs", deselect "Enable Unite" and store your config. The form is giant, so you might want to Search the page for the proper setting.
As I don't have any use for Opera Unite anyways this is a working solution for me, however I am still curios why the availability of one UPnP-Server would disable the other.