At Uppsala universitet there are currently open positions as mathematics postdoc and as researchers. The announcement texts are identical, aside from this part (and clarification on it) that is missing from the researcher position:
To be eligible for a position as postdoctoral researcher the applicant's PhD degree must have been obtained no more than three years prior to the application date; however, for example periods of sick leave or parental leave are deducted from the three-year period.
What is the difference between researcher and postdoc in the Swedish system in general, or Uppsala university in specific?