Hi, welcome to GoY, Tolmiea menziesii should be grown in full to partial shade, and are totally hardy to 5 f and lower, so are better off planted in the garden, in a north or east facing position, in moist but well drained soil rich in humus, so being in a pot, in front of a window, is probably not the best place for it, if it has to be in a pot, try placing it in a shaded spot in a cool room, Derek.

I think it's a watering issue. The number 1 reason for the leaf edges to brown up like that is over watering. 'Killing it with kindness' as they say. I know the plant likes a moist condition, but maybe let the soil 'nearly' dry out before the next watering. Try to avoid getting the leaves wet. Does that pot have a drainage hole? That's critical. If not just take a power drill to it. All other conditions seem ideal for this plant to thrive. These plants are vigorous & require only minimal care - they grow in Alaska. You can easily propagate a new plant, by sticking healthy leaves into most soil.