Thanks to @chidea’s lead, I’ve found a definitive solution.
Adobe Illustrator CC has an option (enabled by default) to save SVG as “responsive” (that is, scalable in web pages).
Just click on the “More Options” button on the Save pane, while saving as a Tiny 1.2 SVG, and deselect “responsive”. Then the file will load correctly with Fritzing without the need to edit it.
Thanks to
https://github.com/filamentgroup/grunticon/issues/127