diff --git a/devtools/client/shared/test/browser_inplace-editor_maxwidth.js b/devtools/client/shared/test/browser_inplace-editor_maxwidth.js
index 2524ff43c9c6..c68666ef7f76 100644
--- a/devtools/client/shared/test/browser_inplace-editor_maxwidth.js
+++ b/devtools/client/shared/test/browser_inplace-editor_maxwidth.js
@@ -97,7 +97,7 @@ const testMaxWidth = async function(editor) {
function getLines(textarea) {
const win = textarea.ownerDocument.defaultView;
const style = win.getComputedStyle(textarea);
- return Math.floor(textarea.clientHeight / parseFloat(style.lineHeight));
+ return Math.floor(textarea.clientHeight / parseFloat(style.fontSize));
}
/**
diff --git a/layout/reftests/bugs/reftest.list b/layout/reftests/bugs/reftest.list
index bc2a5915f089..7d5d881e3d58 100644
--- a/layout/reftests/bugs/reftest.list
+++ b/layout/reftests/bugs/reftest.list
@@ -652,7 +652,7 @@ asserts(4) == 368155-negative-margins-1.html 368155-negative-margins-1-ref.html
== 370629-1.html 370629-1-ref.html
== 370629-2.html 370629-2-ref.html
== 370692-1.xhtml 370692-1-ref.xhtml
-== 371041-1.html 371041-1-ref.html
+pref(layout.css.line-height.normal-as-resolved-value.enabled,false) == 371041-1.html 371041-1-ref.html
== 371043-1.html 371043-1-ref.html
== 371354-1.html 371354-1-ref.html
== 371483-1.html about:blank # assertion test
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 7b613ba23d22..cc79361c2825 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -2104,8 +2104,17 @@ bool nsComputedDOMStyle::GetLineHeightCoord(nscoord& aCoord) {
AssertFlushedPendingReflows();
nscoord blockHeight = NS_UNCONSTRAINEDSIZE;
- if (StyleText()->mLineHeight.IsMozBlockHeight()) {
- if (!mInnerFrame) return false;
+ const auto& lh = StyleText()->mLineHeight;
+
+ if (lh.IsNormal() &&
+ StaticPrefs::layout_css_line_height_normal_as_resolved_value_enabled()) {
+ return false;
+ }
+
+ if (lh.IsMozBlockHeight()) {
+ if (!mInnerFrame) {
+ return false;
+ }
if (nsLayoutUtils::IsNonWrapperBlock(mInnerFrame)) {
blockHeight = mInnerFrame->GetContentRect().height;
diff --git a/modules/libpref/init/StaticPrefList.h b/modules/libpref/init/StaticPrefList.h
index d3ba68d5c88c..03ca3afab8fd 100644
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -5435,6 +5435,34 @@ VARCACHE_PREF(
bool, true
)
+// Whether the computed value of line-height: normal returns the `normal`
+// keyword rather than a pixel value based on the first available font.
+//
+// Only enabled on Nightly and early beta, at least for now.
+//
+// NOTE(emilio): If / when removing this pref, the GETCS_NEEDS_LAYOUT_FLUSH flag
+// should be removed from line-height (and we should let -moz-block-height
+// compute to the keyword as well, which shouldn't be observable anyway since
+// it's an internal value).
+//
+// It'd be nice to make numbers compute also to themselves, but it looks like
+// everybody agrees on turning them into pixels, see the discussion starting
+// from [1].
+//
+// [1]: https://github.com/w3c/csswg-drafts/issues/3749#issuecomment-477287453
+#ifdef EARLY_BETA_OR_EARLIER
+#define PREF_VALUE true
+#else
+#define PREF_VALUE false
+#endif
+VARCACHE_PREF(
+ Live,
+ "layout.css.line-height.normal-as-resolved-value.enabled",
+ layout_css_line_height_normal_as_resolved_value_enabled,
+ bool, PREF_VALUE
+)
+#undef PREF_VALUE
+
//---------------------------------------------------------------------------
// Prefs starting with "media."
//---------------------------------------------------------------------------
diff --git a/testing/web-platform/tests/css/cssom/getComputedStyle-line-height.html b/testing/web-platform/tests/css/cssom/getComputedStyle-line-height.html
new file mode 100644
index 000000000000..089a6d848510
--- /dev/null
+++ b/testing/web-platform/tests/css/cssom/getComputedStyle-line-height.html
@@ -0,0 +1,23 @@
+
+
+CSS Test: line-height resolved value
+
+
+
+
+
+
+
+
+
+
diff --git a/testing/web-platform/tests/html/rendering/replaced-elements/the-select-element/select-1-line-height.html b/testing/web-platform/tests/html/rendering/replaced-elements/the-select-element/select-1-line-height.html
index e6383f089ffa..605a988e255c 100644
--- a/testing/web-platform/tests/html/rendering/replaced-elements/the-select-element/select-1-line-height.html
+++ b/testing/web-platform/tests/html/rendering/replaced-elements/the-select-element/select-1-line-height.html
@@ -26,9 +26,10 @@ select { line-height:100px; }