The field of research is the biological sciences.
Graduate student B worked on the project for 2 years: he did experiments to gather genome-wide data and analyzed part of that data. He defined the direction and feasibility of the project, and developed the methodology; if it were not to him, there wouldn't be a paper.
Post-doc A picked up the project for 1 year after graduate student B left the lab, analyzed the data, wrote the paper, contributed 4 key figures (exactly half of the figures) and at least half of the scientific conclusions.
It was agreed upon that A and B would be co-first authors, but currently they are listed as B, A, et al.
Do you think A would be entitled to feel some kind of injustice at not having his name listed in alphabetical order? Is there a consensus that co-first authors should be in alphabetical order and is the editor likely to point this out?
 Additional information: In this field, you can specify 'co-first authors' at the time of submission, and it is written as such under the author's list on the final publication as "X an Y have contributed equally to this work". Which of course is a big source of conflict.