Works great. Enables you to save a portion (or the visible region) of a webpage to SVG. Renders the visible elements into SVG fairly accurately. Obviously, since it has to convert what Gecko renders to an equivalent in SVG, it is not always 100% match (e.g. shadows are problematic, CSS blur does not work at all). But that is understandable, the capabilities of CSS and those of SVG are not 1:1, each can do a bit different things visually and matching them 1:1 is probably pretty hard, I can imagine.
BTW, the text parts of the page are kept as text so the screenshots can be manupulated, e.g., in Inkscape as needed. So good job, Mr. Becker; compared to what I've seen and tested in this category of add-ons, this is the best one I found by far.

Doesn't properly render a local file that I tested. Additionally, whether the viewport option captures the entire page or merely the visible portion isn't evident.

Doesn't work. Throws some error. Waste of time. Move along.

not working on https://mindmapp.cedoor.dev/app

the text in nodes dissappear

I liked the add-on, but valued it 4 stars because it captures only the visible part of a page. If you mend it to take a shot of the whole page including areas which can be reached by scrolling, then I make it 5 stars.