--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -803,16 +803,17 @@ xul|filefield + xul|button {
 
 html|select[size][multiple],
 xul|richlistbox,
 xul|listbox {
   -moz-appearance: none;
   margin-inline-start: 0;
   background-color: var(--in-content-box-background);
   border: 1px solid var(--in-content-box-border-color);
+  border-radius: 2px;
   color: var(--in-content-text-color);
 }
 
 html|select[size][multiple] > html|option,
 xul|treechildren::-moz-tree-row,
 xul|listbox xul|listitem {
   padding: 0.3em;
   margin: 0;
@@ -834,16 +835,17 @@ xul|listbox xul|listitem[selected="true"
 }
 
 /* Trees */
 
 xul|tree {
   -moz-appearance: none;
   font-size: 1em;
   border: 1px solid var(--in-content-box-border-color);
+  border-radius: 2px;
   background-color: var(--in-content-box-background);
   margin: 0;
 }
 
 xul|tree:-moz-focusring,
 xul|richlistbox:-moz-focusring {
   border: 1px dotted var(--in-content-border-focus);
 }