I find it strange that Firefox could be at fault as I am running FireFox 2.0.0.6 and 12 add-ons on a Rev A iMac G5 and no issues as such what so ever.

Full circle folders seem to contains cache files for the mozilla apps

I am after the problems I have been through going more towards the power supply and logic board which are both fully covered under a extended warranty program and if they need to be replaced will be free of any charge.

This message and all previous from me this year have been done using Firefox Browser and I have never seen any issues.

The info I suggested above is just basic Trouble shooting till he can get to an Apple dealer so at least he can say tried that done that.

I tend to agree that it may be a hardware issue ... not so much MB or PS as it is only happening under Firefox per his description.

But the other Item I would consider is a bad memory module that gets hit by the overhead of Firefox when in use. The reasons for that is I have a client that had one bad memory module on a G5 (5G Ram) that would crash his system (similar to described above) shortly after opening up a different memory hog app. Took some tool testing apps to actually find the faulty module but once replaced the machine is not missing a beat now.

It could be a possibilty of the ram very much so. Or one of the two ram slots has gone or is going bad which means the logic board it cactus pretty much.

I have checked the memory usuage of firefox for me included with 12 addons and a theme and it is using 23.80 cpu which goes up and down and real memory anywhere from 80 - 96% and sometimes lower and higher.

I've never known bad RAM to shut down a system, but a dodgy motherboard, yes.

I have seen bad ram cause Kernal Panics a few times but never an actual shutdown.

I would also like to know if the iMac slows down suddenly for no apparent reason this is another sign of a bad or going bad logic board.

I have seen a number of things when this happens.

Happened to me just ~6 weeks ago. Started with corrupt file transfers (over a LAN), then a few days later, Safari and Firefox unexpectedly started quitting followed by kernel panics a couple of days after that. I identified the stick and chucked it.

Kernel panics, absolutely. But complete and random shutdown?

In the words of Ron Burgundy, "I'm not even angry, I'm impressed!"

Fair point. I haven't heard of it happening either.

I know it was strange about it shutting down due to a bad ram module, but as the stick was within the first slot pair (memory on the G5 has to be in pairs of course), it appeared that when the system burped and tried to find the memory reference for whatever purpose (that was originally written to the bad memory module) the fans would also start spinning up and it was like a jet plane flying over at low altitude.

My thought is that due to it not actually causing a kernel panic (which is what I would have expected also) some instruction somewhere within the OS or memory was trying to find the next jump and started the hard drives spinning looking for what it could not find which in turn may have started up the fans trying to cool down the system. If things get hot enough inside fortunately the heat sensors on board will usually (if I remember right on the newer boards introduced with the G5's) trip a sudo type circuit breaker (that resets after a short time) built into the MB or PS somewhere.

The other possibility which I have also seen although it was on a yuk PC server (it took me over 5 months to get the factory rep to take it to their facility to verify what I had already suspected). It turned out it was a bad trace on the MB. When internal case heat got to a certain temperature level (yes the server was in a climate controlled room also) it would open and thus the Server would shut down. With the aforementioned Jets and excessive HD spinning there may also be such a weak trace within this MB on the G5 but after replacing the memory module again it has been running like a champ with no shut downs.

Anything is possible in technology even the arcane.

Ok, have gone for roughly a week not using Firefox. Not one single shut down.
Fired up Firefox this morning. Bang! Shutdown within half an hour.

FF is fully up to date. Deleted it (and all associated prefs etc), re-installed it (new download) and made sure it was up to date. 10 minutes later, (nothing else was open in the background) it shut down again.

I have now uninstalled it… It makes no sense to me, so I have gotten rid of it for now until I can figure something else out.