diff --git a/phpBB/admin/page_header_admin.php b/phpBB/admin/page_header_admin.php
index 73e6757b34..87ff439a7a 100644
--- a/phpBB/admin/page_header_admin.php
+++ b/phpBB/admin/page_header_admin.php
@@ -35,7 +35,9 @@ if ( $board_config['gzip_compress'] )
 {
 	$phpver = phpversion();
 
-	if ( $phpver >= '4.0.4pl1' && strstr($HTTP_USER_AGENT,'compatible') )
+	$useragent = (isset($_SERVER["HTTP_USER_AGENT"]) ) ? $_SERVER["HTTP_USER_AGENT"] : $HTTP_USER_AGENT;
+
+	if ( $phpver >= '4.0.4pl1' && ( strstr($useragent,'compatible') || strstr($useragent,'Gecko') ) )
 	{
 		if ( extension_loaded('zlib') )
 		{
@@ -129,4 +131,4 @@ $template->assign_vars(array(
 
 $template->pparse('header');
 
-?>
\ No newline at end of file
+?>
diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index ea5b6bb8fb..e35afeb7e8 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -138,6 +138,7 @@ h3 {font-size:12pt;color:blue}
 <li>Fixed incomplete deletion of PMs when removing the associated user</li>
 <li>Fixed unread and new PM user counters to decrement appropriately in all situations</li>
 <li>Fixed possible cross-site scripting issue with username search</li>
+<li>Fixed some problems with gzip in combination with newer PHP versions and Mozilla</li>
 <li></li>
 </ul>
 
diff --git a/phpBB/includes/page_header.php b/phpBB/includes/page_header.php
index e90783d9d5..7ba0a31696 100644
--- a/phpBB/includes/page_header.php
+++ b/phpBB/includes/page_header.php
@@ -35,7 +35,9 @@ if ( $board_config['gzip_compress'] )
 {
 	$phpver = phpversion();
 
-	if ( $phpver >= '4.0.4pl1' && strstr($HTTP_USER_AGENT,'compatible') )
+	$useragent = (isset($_SERVER["HTTP_USER_AGENT"]) ) ? $_SERVER["HTTP_USER_AGENT"] : $HTTP_USER_AGENT;
+
+	if ( $phpver >= '4.0.4pl1' && ( strstr($useragent,'compatible') || strstr($useragent,'Gecko') ) )
 	{
 		if ( extension_loaded('zlib') )
 		{