I would like to humbly suggest that as .stl files are becoming ubiquitous to many, that Firefox should consider embedding an stl viewer into the browser and possibly even with 3D rotation capability but maybe that's asking too much!
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Seconded! It's very useful being able to view the STL files directly in Safari...
eg: https://github.com/MotorDynamicsLab/LDOVoron2/blob/main/STLs/z_belt_cover_a_led.stl
never-displayed