The first step was getting the timing values, and I must say that it's really crazy how every project is always stating "it's easy, you just have to install this", and that means that you have to install php for one project, the different .net frameworks for another, other request Java, then the jdk, jre, ant, ...., in this case they say that you just have to install both Cygwin and Python in order to get the time!!!
I'm tired of installing things, so I opted to use the macbook and fortunately it seems that Python is already installed in MacOsX so I didn't need to install anything and after a few tests I got the timing values (although I wasn't sure about the unmount part and skipped that script because I didn't want to get a big problem).
Ok, around 1500ms with the default profile. So I disabled some add-ons and got down to 1000ms, wow, 50% improvement.
Then I checked both WriteArea and SendToPhone (the current as the next one that includes some drastic changes) and it seems that the startup time was similar, I didn't notice a performance hit due to enabling or disabling the extensions, and that's logical because they don't really do too much things at startup, just some listener for context menus, an overlay here and there,... but no heavy duty. That means that fortunately I don't have to work in order to improve the performance.
Finally I started re-enabling the rest of extensions and checking the times and the culprit for the 500ms hit is.... Firebug!
I don't want to say bad words about Firebug because it's really useful, but on the other hand it really needs some hard work with cooperation by the Mozilla guys to find out the issues and address them correctly.