Hi Alluziion,
They are indeed two different concepts. I used to use pixels until i point things got complicated and switched to percentages.
To get started on my research in earnest,i googled for mozilla css extensions and i discovered the flexible boxes. The box has the property flex-flow and flex-shrink.One reason i like flex-box is that it claims to of help if you wish to predict how your space will be utilised.
I haven't tried it yet but i will starting tomorrow.