I’m printing the first “Thing” I’ve designed in FreeCad. I need to play with retraction settings more but one of the first lessons learnt was lay out Construction Lines that replicate the build surface, that way you know it’s going to fit. Attempt one was too long and had a corner just slipping off the Kossel Mini mirror bed.
It did go from FreeCad STL to Slic3r for printing.
I would try more retrack and higher travel speeds.
you would be amazed just how different a print can look just by using different software.
Try a reprint using Cura, I never get stringing like that, in fact I never get stringing. Cura tries to retrace it’s path most of the time rather than take the shortest route.