diff --git a/layout/reftests/font-inflation/fixed-width-viewport-inflation-ref.html b/layout/reftests/font-inflation/fixed-width-viewport-inflation-ref.html
new file mode 100644
index 000000000000..6a5356c6e078
--- /dev/null
+++ b/layout/reftests/font-inflation/fixed-width-viewport-inflation-ref.html
@@ -0,0 +1,18 @@
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diff --git a/layout/reftests/font-inflation/fixed-width-viewport-inflation.html b/layout/reftests/font-inflation/fixed-width-viewport-inflation.html
new file mode 100644
index 000000000000..935f2e4bcd76
--- /dev/null
+++ b/layout/reftests/font-inflation/fixed-width-viewport-inflation.html
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diff --git a/layout/reftests/font-inflation/fixed-width-viewport-no-inflation.html b/layout/reftests/font-inflation/fixed-width-viewport-no-inflation.html
new file mode 100644
index 000000000000..35f6bd3d43d9
--- /dev/null
+++ b/layout/reftests/font-inflation/fixed-width-viewport-no-inflation.html
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Some uninflated text.
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diff --git a/layout/reftests/font-inflation/reftest.list b/layout/reftests/font-inflation/reftest.list
index e460bfe6b3b4..7f73464b1f20 100644
--- a/layout/reftests/font-inflation/reftest.list
+++ b/layout/reftests/font-inflation/reftest.list
@@ -69,6 +69,10 @@ test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceE
test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == form-button-fixed-height.html form-button-fixed-height-ref.html
test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == form-button-fixed-width.html form-button-fixed-width-ref.html
test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == form-button.html form-button-ref.html
+test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == fixed-width-viewport-no-inflation.html fixed-width-viewport-no-inflation.html
+fails asserts(0-2) pref(layout.css.devPixelsPerPx,"0.5") test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == fixed-width-viewport-no-inflation.html fixed-width-viewport-no-inflation.html
+test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == fixed-width-viewport-inflation.html fixed-width-viewport-inflation-ref.html
+fails skip-if(Android&&webrender||cocoaWidget) asserts(0-2) pref(layout.css.devPixelsPerPx,"2.0") test-pref(font.size.inflation.emPerLine,15) test-pref(font.size.inflation.forceEnabled,true) test-pref(font.size.inflation.lineThreshold,0) == fixed-width-viewport-inflation.html fixed-width-viewport-inflation-ref.html
# Ordinarily, reftests use a browser.viewport.desktopWidth of 800px, same as the
# size of the reftest document. The failure condition of the test below however