In my experience using first person in abstract or even in the manuscript is field- as well as individual- dependent. Prof. John Cochrane (when he was at U of Chicago) advised not to use royal pronoun "we" when it's a single author paper. In business management you can see a mix of use of "we" even when the paper is written by a single author. Some journals like Journal of Marketing require all the abstracts in third person (e.g., the authors find xyz instead of we find xyz) but don't have any rules about using I/we in the manuscript.