I downvoted this post and then thought i'd better reply because its possible carol is new to programming and didn't realise that the clever reply was just that .. clever .. but not intelligent.
Any functionality within a program needs to load code to implement that functionality. The process of loading that code will take time. It's possible to optimise the loading of the code so it appears that the system loads fast, but in all cases that code has to be loaded at some point. When the code is loaded is part of the the compromise and trade off.
Any add on adds to the functionality. Opera may have all the functionality of all the add ons that you would ever want in FireFox without having to use an add on but it *still* has to load that code. Having said that, Opera has an add on architecture .. just it bundles some of the stuff FF views as an add on into the system.
It is likely, therefore, that Opera itself has to have made trade offs .. what functionality can it do without in order to speed up the start up (Or to put it simply .. what code can it avoid loading at start up?).
Now i know Opera has a built in debugger. But i can bet you that Opera has made compomises concerning the loading and running of this debugger at start up because, lets face it, very few people outside the esteemed readers of this publication are going to need or use a debugger so it actually doesn't *have* to be loaded so .. oh dear .. I've just made a compromise, haven't I?
Opera, IE, Safri, Firefox will all induldge in trade offs. Which architecture you choose is a matter of personal taste and browser religion. Just don't try and be too clever about it.