--- a/browser/themes/shared/incontentprefs/preferences.inc.css
+++ b/browser/themes/shared/incontentprefs/preferences.inc.css
@@ -99,16 +99,20 @@ separator.thin:not([orient="vertical"]) 
   white-space: nowrap;
 }
 
 .accessory-button {
   min-width: 145px;
   margin: 2px 0;
 }
 
+#searchInput {
+  border-radius: 0;
+}
+
 /* Subcategory title */
 
 /**
  * The first subcategory title for each category should not have margin-top.
  */
 
 .subcategory:not([hidden]) ~ .subcategory {
   margin-top: 32px;

--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -757,27 +757,23 @@ xul|*.fileFieldIcon {
   margin-inline-end: 0;
 }
 
 xul|*.fileFieldLabel {
   margin-inline-start: -26px;
   padding-inline-start: 36px;
 }
 
-xul|textbox:-moz-locale-dir(rtl),
 xul|*.fileFieldLabel:-moz-locale-dir(rtl),
-xul|textbox + xul|button:-moz-locale-dir(ltr),
 xul|filefield + xul|button:-moz-locale-dir(ltr) {
   border-top-left-radius: 0;
   border-bottom-left-radius: 0;
 }
 
-xul|textbox:-moz-locale-dir(ltr),
 xul|*.fileFieldLabel:-moz-locale-dir(ltr),
-xul|textbox + xul|button:-moz-locale-dir(rtl),
 xul|filefield + xul|button:-moz-locale-dir(rtl) {
   border-top-right-radius: 0;
   border-bottom-right-radius: 0;
 }
 
 xul|filefield + xul|button {
   border-inline-start: none;
 }