(It's possible that this is an error in the SVG (and there does appear to be extraneous markup), however it appears correctly in Edge and in some situations in Firefox.)

The image at https://fathy.fr/assets/5c8a82454a84da5af9a2.svg appears to have several copies of the image duplicated over itself. This appears to be from several elements along the lines of <g transform="translate(x y)">, so it's coming from somwhere, but when rendered in Edge and when embedded in another page (https://fathy.fr/html2svg) they are not visible.

Tested in a recent nightly and a build from a year or so ago, so it doesn't appear to be a regression.

(Also interesting, but completely unrelated: apparently the built-in screenshot tool in Firefox will not take a screenshot of a page that is just an SVG. )

Because Firefox does not support feImage filters that point to fragments.

Here's the testcase itself, for archival purposes.

Hmm, interestingly the testcase works if we load it as an image (e.g. in Bugzilla's "overlay" visualization that it uses when you click on bugzilla attachments, or at this data URI:

data:text/html,<img src="https://bugzilla.mozilla.org/attachment.cgi?id=9303230">

But it does reproduce if you load the image in its own tab (by e.g. ctrl-clicking the attachment link)

If you delete the problematic feImage elements in the filters it works too.