Hi Melody, There isn't a setting for this that you can adjust -- instead it is simply broken on Catalina, as discussed in this previous post (and the ones before it in the thread). <http://plato.cgl.ucsf.edu/pipermail/chimera-users/2020-May/016845.html> In that thread, Tom suggests using ChimeraX instead, which does not have the problem. But it depends what assortment of tools in Chimera you were planning to use. Many have equivalents in ChimeraX, but some that don't are listed in the "missing features" section of the ChimeraX download page: <http://www.rbvi.ucsf.edu/chimerax/download.html> Sorry about that, Elaine ----- Elaine C. Meng, Ph.D. UCSF Chimera(X) team Department of Pharmaceutical Chemistry University of California, San Francisco

On Jun 22, 2020, at 7:35 PM, Melody Campbell <melcam@umich.edu> wrote:

Hi, Since I installed the 64-bit UCSF Chimera version for Mac Catalina (10.15.5) each time I open a new map, a new instance of UCSF Chimera opens instead of opening the map in the same instance. Could you help me find where the setting is to change this so that by default all new maps and models opened (via double clicking icons) is done in the same instance of Chimera? (I tried re-installing/ restoring all factory settings and deleting my /Users/user/.chimera/preferences file, but still by default, a new session opens for each map). Thanks so much! Melody