diff --git a/phpBB/styles/prosilver/template/forum_fn.js b/phpBB/styles/prosilver/template/forum_fn.js
index 0da3c77d53..23dfae9fab 100644
--- a/phpBB/styles/prosilver/template/forum_fn.js
+++ b/phpBB/styles/prosilver/template/forum_fn.js
@@ -451,6 +451,31 @@ function toggle_dropdown()
 
 	options.dropdown.toggle();
 	parent.toggleClass(options.visibleClass, !visible).toggleClass('dropdown-visible', !visible);
+
+	// Check dimensions when showing dropdown
+	// !visible because variable shows state of dropdown before it was toggled
+	if (!visible) {
+		options.dropdown.find('.dropdown-contents').each(function() {
+			var $this = $(this),
+				windowWidth = $(window).width();
+
+			$this.css({
+				marginLeft: 0,
+				left: 0,
+				maxWidth: (windowWidth - 4) + 'px'
+			});
+
+			var offset = $this.offset().left,
+				width = $this.outerWidth(true);
+
+			if (offset < 2) {
+				$this.css('left', (2 - offset) + 'px');
+			}
+			else if ((offset + width + 2) > windowWidth) {
+				$this.css('margin-left', (windowWidth - offset - width - 2) + 'px');
+			}
+		});
+	}
 }
 
 /**
diff --git a/phpBB/styles/prosilver/theme/common.css b/phpBB/styles/prosilver/theme/common.css
index 9e15eada22..bc2432e2a4 100644
--- a/phpBB/styles/prosilver/theme/common.css
+++ b/phpBB/styles/prosilver/theme/common.css
@@ -510,6 +510,10 @@ ul.linklist.bulletin li.no-bulletin:before {
 	border: 1px solid transparent;
 	border-radius: 5px;
 	padding: 5px;
+	position: relative;
+	-webkit-box-sizing: border-box;
+	-moz-box-sizing: border-box;
+	box-sizing: border-box;
 }
 
 .dropdown li {
diff --git a/phpBB/styles/prosilver/theme/content.css b/phpBB/styles/prosilver/theme/content.css
index ad6f27665d..389f93fa4e 100644
--- a/phpBB/styles/prosilver/theme/content.css
+++ b/phpBB/styles/prosilver/theme/content.css
@@ -516,6 +516,7 @@ blockquote .codebox {
 	padding: 6px;
 	border: 1px dashed transparent;
 	clear: left;
+	-webkit-box-sizing: border-box;
 	-moz-box-sizing: border-box;
 	box-sizing: border-box;
 }