Created attachment 506968 [details] Plain HTML test case When we have an SVG fragment that is not rendered because it or a parent is display:none, attempts to fetch the value of any percentage-based lengths in user units (by calling SVGLength.value) do not return the expected result. In the attached test case we have a circle with cy="50%" but querying the value of this length in user units gives us "5.000000245224396e-21" instead of 50. Not that if we change the block from "display:none" to "visibility:hidden" the result is 50 as expected. This situation occurs frequently in our mochitest suite where the test content appears in a display:none block.
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