diff --git a/src/libslic3r/Format/SL1.cpp b/src/libslic3r/Format/SL1.cpp
index 64cb8b815..4038cb046 100644
--- a/src/libslic3r/Format/SL1.cpp
+++ b/src/libslic3r/Format/SL1.cpp
@@ -248,7 +248,7 @@ std::vector<ExPolygons> extract_slices_from_sla_archive(
     {
         double          incr, val, prev;
         bool            stop = false;
-        tbb::spin_mutex mutex;
+        tbb::spin_mutex mutex = {};
     } st {100. / slices.size(), 0., 0.};
 
     tbb::parallel_for(size_t(0), arch.images.size(),
@@ -371,6 +371,13 @@ void fill_iniconf(ConfMap &m, const SLAPrint &print)
     m["numSlow"]      = std::to_string(stats.slow_layers_count);
     m["numFast"]      = std::to_string(stats.fast_layers_count);
     m["printTime"]    = std::to_string(stats.estimated_print_time);
+
+    bool hollow_en = false;
+    auto it = print.objects().begin();
+    while (!hollow_en && it != print.objects().end())
+        hollow_en = (*it++)->config().hollowing_enable;
+
+    m["hollow"] = hollow_en ? "1" : "0";
     
     m["action"] = "print";
 }
diff --git a/t/flow.t b/t/flow.t
index 4d7ee5ca2..50c491604 100644
--- a/t/flow.t
+++ b/t/flow.t
@@ -21,7 +21,7 @@ use Slic3r::Test;
     $config->set('fill_density', 0.4);
     $config->set('bottom_solid_layers', 1);
     $config->set('first_layer_extrusion_width', 2);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('filament_diameter', [ 3.0 ]);
     $config->set('nozzle_diameter', [ 0.5 ]);
     
diff --git a/t/layers.t b/t/layers.t
index a9f7dfe39..4d958808a 100644
--- a/t/layers.t
+++ b/t/layers.t
@@ -49,7 +49,7 @@ use Slic3r::Test qw(_eq);
     $config->set('first_layer_height', 0.2);
     ok $test->(), "absolute first layer height";
 
-    $config->set('first_layer_height', '60%');
+    $config->set('first_layer_height', 0.6 * $config->layer_height);
     ok $test->(), "relative first layer height";
 
     $config->set('z_offset', 0.9);
diff --git a/t/multi.t b/t/multi.t
index 8e7225bec..e74a7a1a8 100644
--- a/t/multi.t
+++ b/t/multi.t
@@ -181,7 +181,7 @@ use Slic3r::Test;
     my $config = Slic3r::Config::new_from_defaults;
     $config->set('nozzle_diameter', [0.6,0.6,0.6,0.6]);
     $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('skirts', 0);
     my $print = Slic3r::Test::init_print($model, config => $config);
     
diff --git a/t/shells.t b/t/shells.t
index 47b5c8881..29bc0b5f0 100644
--- a/t/shells.t
+++ b/t/shells.t
@@ -84,7 +84,7 @@ use Slic3r::Test;
 {
     my $config = Slic3r::Config::new_from_defaults;
     $config->set('layer_height', 0.3);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('bottom_solid_layers', 0);
     $config->set('top_solid_layers', 3);
     $config->set('cooling', [ 0 ]);
@@ -119,7 +119,7 @@ use Slic3r::Test;
     $config->set('cooling', [ 0 ]);             # prevent speed alteration
     $config->set('first_layer_speed', '100%');  # prevent speed alteration
     $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('extrusion_width', 0.55);
     $config->set('bottom_solid_layers', 3);
     $config->set('top_solid_layers', 0);
@@ -142,7 +142,7 @@ use Slic3r::Test;
     $config->set('cooling', [ 0 ]);             # prevent speed alteration
     $config->set('first_layer_speed', '100%');  # prevent speed alteration
     $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('bottom_solid_layers', 3);
     $config->set('top_solid_layers', 3);
     $config->set('solid_infill_speed', 99);
@@ -170,7 +170,7 @@ use Slic3r::Test;
     $config->set('spiral_vase', 1);
     $config->set('bottom_solid_layers', 0);
     $config->set('skirts', 0);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('start_gcode', '');
     $config->set('temperature', [200]);
     $config->set('first_layer_temperature', [205]);
@@ -231,8 +231,8 @@ use Slic3r::Test;
     $config->set('bottom_solid_layers', 0);
     $config->set('retract_layer_change', [0]);
     $config->set('skirts', 0);
-    $config->set('first_layer_height', '100%');
     $config->set('layer_height', 0.4);
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('start_gcode', '');
 #    $config->set('use_relative_e_distances', 1);
     $config->validate;
@@ -310,7 +310,7 @@ use Slic3r::Test;
 #    $config->set('spiral_vase', 1);
 #    $config->set('bottom_solid_layers', 0);
 #    $config->set('skirts', 0);
-#    $config->set('first_layer_height', '100%');
+#    $config->set('first_layer_height', $config->layer_height);
 #    $config->set('start_gcode', '');
 #    
 #    my $print = Slic3r::Test::init_print('two_hollow_squares', config => $config);
diff --git a/t/thin.t b/t/thin.t
index 9147236ee..50e7abc95 100644
--- a/t/thin.t
+++ b/t/thin.t
@@ -18,7 +18,7 @@ use Slic3r::Test;
 if (0) {
     my $config = Slic3r::Config::new_from_defaults;
     $config->set('layer_height', 0.2);
-    $config->set('first_layer_height', '100%');
+    $config->set('first_layer_height', $config->layer_height);
     $config->set('extrusion_width', 0.5);
     $config->set('first_layer_extrusion_width', '200%'); # check this one too
     $config->set('skirts', 0);
diff --git a/tests/fff_print/test_flow.cpp b/tests/fff_print/test_flow.cpp
index 08ba15a84..dc73f4b6e 100644
--- a/tests/fff_print/test_flow.cpp
+++ b/tests/fff_print/test_flow.cpp
@@ -24,7 +24,7 @@ SCENARIO("Extrusion width specifics", "[Flow]") {
 			{ "skirts",				1 },
 			{ "perimeters",			3 },
 			{ "fill_density",		"40%" },
-			{ "first_layer_height", "100%" }
+			{ "first_layer_height", 0.3 }
 			});
 
         WHEN("first layer width set to 2mm") {
diff --git a/tests/libslic3r/test_placeholder_parser.cpp b/tests/libslic3r/test_placeholder_parser.cpp
index e632dc705..8c56afc6d 100644
--- a/tests/libslic3r/test_placeholder_parser.cpp
+++ b/tests/libslic3r/test_placeholder_parser.cpp
@@ -14,9 +14,12 @@ SCENARIO("Placeholder parser scripting", "[PlaceholderParser]") {
 	    { "nozzle_diameter", "0.6;0.6;0.6;0.6" },
 	    { "temperature", "357;359;363;378" }
 	});
-    // To test the "first_layer_extrusion_width" over "first_layer_heigth" over "layer_height" chain.
-    config.option<ConfigOptionFloatOrPercent>("first_layer_height")->value = 150.;
-    config.option<ConfigOptionFloatOrPercent>("first_layer_height")->percent = true;
+    // To test the "first_layer_extrusion_width" over "first_layer_heigth".
+    // "first_layer_heigth" over "layer_height" is no more supported after first_layer_height was moved from PrintObjectConfig to PrintConfig.
+//  config.option<ConfigOptionFloatOrPercent>("first_layer_height")->value = 150.;
+//  config.option<ConfigOptionFloatOrPercent>("first_layer_height")->percent = true;
+    config.option<ConfigOptionFloatOrPercent>("first_layer_height")->value = 1.5 * config.opt_float("layer_height");
+    config.option<ConfigOptionFloatOrPercent>("first_layer_height")->percent = false;
     // To let the PlaceholderParser throw when referencing first_layer_speed if it is set to percent, as the PlaceholderParser does not know
     // a percent to what.
     config.option<ConfigOptionFloatOrPercent>("first_layer_speed")->value = 50.;
@@ -50,7 +53,7 @@ SCENARIO("Placeholder parser scripting", "[PlaceholderParser]") {
     SECTION("math: int(-13.4)") { REQUIRE(parser.process("{int(-13.4)}") == "-13"); }
 
     // Test the "coFloatOrPercent" and "xxx_extrusion_width" substitutions.
-    // first_layer_extrusion_width ratio_over first_layer_heigth ratio_over layer_height
+    // first_layer_extrusion_width ratio_over first_layer_heigth.
     SECTION("perimeter_extrusion_width") { REQUIRE(std::stod(parser.process("{perimeter_extrusion_width}")) == Approx(0.67500001192092896)); }
     SECTION("first_layer_extrusion_width") { REQUIRE(std::stod(parser.process("{first_layer_extrusion_width}")) == Approx(0.9)); }
     SECTION("support_material_xy_spacing") { REQUIRE(std::stod(parser.process("{support_material_xy_spacing}")) == Approx(0.3375)); }
diff --git a/xs/t/15_config.t b/xs/t/15_config.t
index 55b679101..4d032019c 100644
--- a/xs/t/15_config.t
+++ b/xs/t/15_config.t
@@ -4,7 +4,7 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 147;
+use Test::More tests => 143;
 
 foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintConfig) {
     $config->set('layer_height', 0.3);
@@ -70,10 +70,11 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     ok abs($config->get('first_layer_height') - 0.3) < 1e-4, 'set/get absolute floatOrPercent';
     is $config->opt_serialize('first_layer_height'), '0.3', 'serialize absolute floatOrPercent';
     
-    $config->set('first_layer_height', '50%');
-    $config->get_abs_value('first_layer_height');
-    ok abs($config->get_abs_value('first_layer_height') - 0.15) < 1e-4, 'set/get relative floatOrPercent';
-    is $config->opt_serialize('first_layer_height'), '50%', 'serialize relative floatOrPercent';
+# This is no more supported after first_layer_height was moved from PrintObjectConfig to PrintConfig.
+#    $config->set('first_layer_height', $config->get('layer_height'));
+#    $config->get_abs_value('first_layer_height');
+#    ok abs($config->get_abs_value('first_layer_height') - 0.15) < 1e-4, 'set/get relative floatOrPercent';
+#    is $config->opt_serialize('first_layer_height'), '50%', 'serialize relative floatOrPercent';
     
     # Uh-oh, we have no point option to test at the moment
     #ok $config->set('print_center', [50,80]), 'valid point coordinates';