Bug 1825050 - Allow scrolling horizontally big preview images. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D173862

browser/base/content/pageinfo/pageInfo.css

@@ -31,6 +31,8 @@
 }
 
 #thepreviewimage {
+  margin: 1em auto;
+  flex: none;
   display: block;
 }
 

browser/base/content/pageinfo/pageInfo.xhtml

@@ -256,7 +256,7 @@
                   oncommand="saveMedia();"/>
         </hbox>
         <vbox id="imagecontainerbox" flex="1">
-          <hbox id="theimagecontainer" pack="center">
+          <hbox id="theimagecontainer">
             <image id="thepreviewimage"/>
           </hbox>
           <hbox id="brokenimagecontainer" pack="center" collapsed="true">

browser/themes/shared/pageInfo.css

@@ -201,10 +201,6 @@ html|input:disabled {
   min-width: 10em;
 }
 
-#thepreviewimage {
-  margin: 1em;
-}
-
 treechildren::-moz-tree-cell-text(broken) {
   font-style: italic;
   color: graytext;