As far as I know the slowdown has appeared since upgrading from Kde 3 to 4. Just what has caused the difference I'm not sure. I have Minime installed on my netbook and FF starts fine, and thats with a slow cpu as well. On my desktop I have 4 ghz memory and 4 core Amd 965 cpu running 3.4ghz. I have had it running at 4.1ghz and FF was still slow. So I don't think it has anything to do with the power of the computer, I think it is something Mozilla have done in the programming somewhere along the way, or something in Kde 4 that it doesn't like. I just Googled "Firefox slow startup time" and there is a LOT of info to look at, so it looks like this is a big problem.