diff --git a/application/palemoon/app/Makefile.in b/application/palemoon/app/Makefile.in
index c0f01212c2..12f28768aa 100644
--- a/application/palemoon/app/Makefile.in
+++ b/application/palemoon/app/Makefile.in
@@ -33,6 +33,14 @@ NSDISTMODE = copy
 
 include $(topsrcdir)/config/config.mk
 
+# If we are trying to show an error dialog about the lack of SSE2 support,
+# make sure that code itself doesn't use SSE2.
+ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+CXXFLAGS := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXXFLAGS))
+CXX := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXX))
+CXXFLAGS += -mno-sse2 -mfpmath=387
+endif
+
 ifeq ($(OS_ARCH),WINNT)
 # Rebuild firefox.exe if the manifest changes - it's included by splash.rc.
 # (this dependency should really be just for firefox.exe, not other targets)
diff --git a/application/palemoon/app/moz.build b/application/palemoon/app/moz.build
index 8b358b6228..044c3e2d16 100644
--- a/application/palemoon/app/moz.build
+++ b/application/palemoon/app/moz.build
@@ -68,3 +68,6 @@ if CONFIG['MOZ_LINKER']:
 
 if CONFIG['HAVE_CLOCK_MONOTONIC']:
     OS_LIBS += CONFIG['REALTIME_LIBS']
+
+if CONFIG['MOZ_LINUX_SSE2_STARTUP_ERROR']:
+    DEFINES['MOZ_LINUX_SSE2_STARTUP_ERROR'] = True
diff --git a/application/palemoon/app/nsBrowserApp.cpp b/application/palemoon/app/nsBrowserApp.cpp
index faf82f710a..041d3fe7f3 100644
--- a/application/palemoon/app/nsBrowserApp.cpp
+++ b/application/palemoon/app/nsBrowserApp.cpp
@@ -40,6 +40,51 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/WindowsDllBlocklist.h"
 
+#ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+#include <cpuid.h>
+#include "mozilla/Unused.h"
+
+static bool
+IsSSE2Available()
+{
+  // The rest of the app has been compiled to assume that SSE2 is present
+  // unconditionally, so we can't use the normal copy of SSE.cpp here.
+  // Since SSE.cpp caches the results and we need them only transiently,
+  // instead of #including SSE.cpp here, let's just inline the specific check
+  // that's needed.
+  unsigned int level = 1u;
+  unsigned int eax, ebx, ecx, edx;
+  unsigned int bits = (1u<<26);
+  unsigned int max = __get_cpuid_max(0, nullptr);
+  if (level > max) {
+    return false;
+  }
+  __cpuid_count(level, 0, eax, ebx, ecx, edx);
+  return (edx & bits) == bits;
+}
+
+static const char sSSE2Message[] =
+    "This browser version requires a processor with the SSE2 instruction "
+    "set extension.\n";
+
+__attribute__((constructor))
+static void
+SSE2Check()
+{
+  if (IsSSE2Available()) {
+    return;
+  }
+  // Using write() in order to avoid jemalloc-based buffering. Ignoring return
+  // values, since there isn't much we could do on failure and there is no
+  // point in trying to recover from errors.
+  MOZ_UNUSED(write(STDERR_FILENO,
+                   sSSE2Message,
+                   MOZ_ARRAY_LENGTH(sSSE2Message) - 1));
+  // _exit() instead of exit() to avoid running the usual "at exit" code.
+  _exit(255);
+}
+#endif
+
 #if !defined(MOZ_WIDGET_COCOA) && !defined(MOZ_WIDGET_ANDROID)
 #define MOZ_BROWSER_CAN_BE_CONTENTPROC
 #include "../../ipc/contentproc/plugin-container.cpp"
diff --git a/application/palemoon/confvars.sh b/application/palemoon/confvars.sh
index 5109c0829b..d1d2ce065a 100644
--- a/application/palemoon/confvars.sh
+++ b/application/palemoon/confvars.sh
@@ -98,6 +98,11 @@ if test "$OS_ARCH" = "WINNT" -o \
   MOZ_BUNDLED_FONTS=1
 fi
 
+# Display an error on non-SSE2 Linux systems
+if test "$OS_ARCH" = "Linux"; then
+  MOZ_LINUX_SSE2_STARTUP_ERROR=1
+fi
+
 # Short-circuit a few services to be removed
 MOZ_MAINTENANCE_SERVICE=
 MOZ_SERVICES_HEALTHREPORT=
diff --git a/browser/app/Makefile.in b/browser/app/Makefile.in
index d807b4337d..cb35ed1fb8 100644
--- a/browser/app/Makefile.in
+++ b/browser/app/Makefile.in
@@ -23,6 +23,14 @@ NSDISTMODE = copy
 
 include $(topsrcdir)/config/config.mk
 
+# If we are trying to show an error dialog about the lack of SSE2 support,
+# make sure that code itself doesn't use SSE2.
+ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+CXXFLAGS := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXXFLAGS))
+CXX := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXX))
+CXXFLAGS += -mno-sse2 -mfpmath=387
+endif
+
 ifeq ($(OS_ARCH),WINNT)
 # Rebuild firefox.exe if the manifest changes - it's included by splash.rc.
 # (this dependency should really be just for firefox.exe, not other targets)
diff --git a/browser/app/moz.build b/browser/app/moz.build
index 1004e280ca..9650761eea 100644
--- a/browser/app/moz.build
+++ b/browser/app/moz.build
@@ -70,6 +70,10 @@ if CONFIG['HAVE_CLOCK_MONOTONIC']:
 if CONFIG['MOZ_GPSD']:
     DEFINES['MOZ_GPSD'] = True
 
+
+if CONFIG['MOZ_LINUX_SSE2_STARTUP_ERROR']:
+    DEFINES['MOZ_LINUX_SSE2_STARTUP_ERROR'] = True
+
 for icon in ('firefox', 'document', 'newwindow', 'newtab', 'pbmode'):
     DEFINES[icon.upper() + '_ICO'] = '"%s/dist/branding/%s.ico"' % (
         TOPOBJDIR, icon)
diff --git a/browser/app/nsBrowserApp.cpp b/browser/app/nsBrowserApp.cpp
index 9cd409cc66..da6d88713e 100644
--- a/browser/app/nsBrowserApp.cpp
+++ b/browser/app/nsBrowserApp.cpp
@@ -40,6 +40,51 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/WindowsDllBlocklist.h"
 
+#ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+#include <cpuid.h>
+#include "mozilla/Unused.h"
+
+static bool
+IsSSE2Available()
+{
+  // The rest of the app has been compiled to assume that SSE2 is present
+  // unconditionally, so we can't use the normal copy of SSE.cpp here.
+  // Since SSE.cpp caches the results and we need them only transiently,
+  // instead of #including SSE.cpp here, let's just inline the specific check
+  // that's needed.
+  unsigned int level = 1u;
+  unsigned int eax, ebx, ecx, edx;
+  unsigned int bits = (1u<<26);
+  unsigned int max = __get_cpuid_max(0, nullptr);
+  if (level > max) {
+    return false;
+  }
+  __cpuid_count(level, 0, eax, ebx, ecx, edx);
+  return (edx & bits) == bits;
+}
+
+static const char sSSE2Message[] =
+    "This browser version requires a processor with the SSE2 instruction "
+    "set extension.\n";
+
+__attribute__((constructor))
+static void
+SSE2Check()
+{
+  if (IsSSE2Available()) {
+    return;
+  }
+  // Using write() in order to avoid jemalloc-based buffering. Ignoring return
+  // values, since there isn't much we could do on failure and there is no
+  // point in trying to recover from errors.
+  MOZ_UNUSED(write(STDERR_FILENO,
+                   sSSE2Message,
+                   MOZ_ARRAY_LENGTH(sSSE2Message) - 1));
+  // _exit() instead of exit() to avoid running the usual "at exit" code.
+  _exit(255);
+}
+#endif
+
 #if !defined(MOZ_WIDGET_COCOA) && !defined(MOZ_WIDGET_ANDROID)
 #define MOZ_BROWSER_CAN_BE_CONTENTPROC
 #include "../../ipc/contentproc/plugin-container.cpp"
diff --git a/browser/confvars.sh b/browser/confvars.sh
index 0343034a41..e8b911da35 100644
--- a/browser/confvars.sh
+++ b/browser/confvars.sh
@@ -18,6 +18,11 @@ if test "$OS_ARCH" = "WINNT"; then
   MOZ_MAINTENANCE_SERVICE=
 fi
 
+# Display an error on non-SSE2 Linux systems
+if test "$OS_ARCH" = "Linux"; then
+  MOZ_LINUX_SSE2_STARTUP_ERROR=1
+fi
+
 # For Basilisk we want to use 52.9.YYYY.MM.DD as MOZ_APP_VERSION in release
 # builds so add-on developers have something to target while maintaining
 # Firefox compatiblity.
diff --git a/old-configure.in b/old-configure.in
index 29d5de7dda..03239e08f6 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -4884,6 +4884,12 @@ if test "$USE_FC_FREETYPE"; then
     fi
 fi
 
+dnl ========================================================
+dnl Check if we need the Linux SSE2 error dialog
+dnl ========================================================
+
+AC_SUBST(MOZ_LINUX_SSE2_STARTUP_ERROR)
+
 dnl ========================================================
 dnl Check for pixman and cairo
 dnl ========================================================