removed directive needed for the PDF preview in FireFox < 78

fixed in https://bugzilla.mozilla.org/show_bug.cgi?id=1582115 and
https://bugzilla.mozilla.org/show_bug.cgi?id=1638826 for FF 78

cfg/conf.sample.php

@@ -87,7 +87,7 @@ languageselection = false
 ;   async functions and display an error if not and for Chrome to enable
 ;   webassembly support (used for zlib compression). You can remove it if Chrome
 ;   doesn't need to be supported and old browsers don't need to be warned.
-; cspheader = "default-src 'none'; base-uri 'self'; form-action 'none'; manifest-src 'self'; connect-src * blob:; script-src 'self' 'unsafe-eval' resource:; style-src 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self' data: blob:; media-src blob:; object-src blob:; sandbox allow-same-origin allow-scripts allow-forms allow-popups allow-modals allow-downloads"
+; cspheader = "default-src 'none'; base-uri 'self'; form-action 'none'; manifest-src 'self'; connect-src * blob:; script-src 'self' 'unsafe-eval'; style-src 'self'; font-src 'self'; frame-ancestors 'none'; img-src 'self' data: blob:; media-src blob:; object-src blob:; sandbox allow-same-origin allow-scripts allow-forms allow-popups allow-modals allow-downloads"
 
 ; stay compatible with PrivateBin Alpha 0.19, less secure
 ; if enabled will use base64.js version 1.7 instead of 2.1.9 and sha1 instead of

lib/Configuration.php

@@ -54,7 +54,7 @@ class Configuration
             'urlshortener'             => '',
             'qrcode'                   => true,
             'icon'                     => 'identicon',
-            'cspheader'                => 'default-src \'none\'; base-uri \'self\'; form-action \'none\'; manifest-src \'self\'; connect-src * blob:; script-src \'self\' \'unsafe-eval\' resource:; style-src \'self\'; font-src \'self\'; frame-ancestors \'none\'; img-src \'self\' data: blob:; media-src blob:; object-src blob:; sandbox allow-same-origin allow-scripts allow-forms allow-popups allow-modals allow-downloads',
+            'cspheader'                => 'default-src \'none\'; base-uri \'self\'; form-action \'none\'; manifest-src \'self\'; connect-src * blob:; script-src \'self\' \'unsafe-eval\'; style-src \'self\'; font-src \'self\'; frame-ancestors \'none\'; img-src \'self\' data: blob:; media-src blob:; object-src blob:; sandbox allow-same-origin allow-scripts allow-forms allow-popups allow-modals allow-downloads',
             'zerobincompatibility'     => false,
             'httpwarning'              => true,
             'compression'              => 'zlib',