--- a/addon-sdk/source/lib/sdk/panel/utils.js
+++ b/addon-sdk/source/lib/sdk/panel/utils.js
@@ -249,20 +249,16 @@ function onPanelClick(event) {
   }
 }
 
 function setupPanelFrame(frame) {
   frame.setAttribute("flex", 1);
   frame.setAttribute("transparent", "transparent");
   frame.setAttribute("autocompleteenabled", true);
   frame.setAttribute("tooltip", "aHTMLTooltip");
-  if (platform === "darwin") {
-    frame.style.borderRadius = "var(--arrowpanel-border-radius, 3.5px)";
-    frame.style.padding = "1px";
-  }
 }
 
 function make(document, options) {
   document = document || getMostRecentBrowserWindow().document;
   let panel = document.createElementNS(XUL_NS, "panel");
   panel.setAttribute("type", "arrow");
   panel.setAttribute("sdkscriptenabled", options.allowJavascript);
 

--- a/browser/extensions/pocket/skin/osx/pocket.css
+++ b/browser/extensions/pocket/skin/osx/pocket.css
@@ -2,12 +2,8 @@
 
 #nav-bar #pocket-button > .toolbarbutton-icon {
 %ifndef MOZ_PHOTON_THEME
   padding: var(--toolbarbutton-inner-padding) 6px;
 %else
   padding: calc(var(--toolbarbutton-inner-padding) - 1px);
 %endif
 }
-
-#PanelUI-pocketView[mainview=true] > .panel-subview-body > #pocket-panel-iframe {
-  border-radius: var(--arrowpanel-border-radius);
-}

--- a/browser/themes/shared/customizableui/customizeMode.inc.css
+++ b/browser/themes/shared/customizableui/customizeMode.inc.css
@@ -566,20 +566,16 @@ toolbarpaletteitem[place=toolbar] > tool
 }
 
 #customization-panelWrapper > .panel-arrowcontent {
   color: var(--arrowpanel-color);
   background: var(--arrowpanel-background);
   background-clip: padding-box;
   border: 1px solid var(--arrowpanel-border-color);
   box-shadow: 0 0 10px hsla(0,0%,0%,.2);
-%ifdef XP_MACOSX
-  -moz-appearance: none;
-  border-radius: var(--arrowpanel-border-radius);
-%endif
 }
 
 #customization-panelWrapper > .panel-arrowbox {
   position: relative;
   height: 10px;
 %ifndef XP_MACOSX
   margin-bottom: 2px;
 %endif

--- a/toolkit/themes/osx/global/global.css
+++ b/toolkit/themes/osx/global/global.css
@@ -15,17 +15,16 @@ menulist > menupopup {
 }
 
 /* ::::: Variables ::::: */
 :root {
   --arrowpanel-padding: 16px;
   --arrowpanel-background: linear-gradient(hsla(0,0%,99%,1), hsla(0,0%,99%,.975) 10%, hsla(0,0%,98%,.975));
   --arrowpanel-color: hsl(0,0%,10%);
   --arrowpanel-border-color: hsla(210,4%,10%,.05);
-  --arrowpanel-border-radius: 3.5px;
   --focus-ring-box-shadow: @focusRingShadow@;
 }
 
 %ifndef MOZ_PHOTON_THEME
 @media (-moz-mac-yosemite-theme) {
   :root {
     --focus-ring-box-shadow: @yosemiteFocusRingShadow@;
   }

--- a/toolkit/themes/osx/global/popup.css
+++ b/toolkit/themes/osx/global/popup.css
@@ -37,17 +37,16 @@ panel[type="arrow"][side="left"],
 panel[type="arrow"][side="right"] {
   margin-top: -25px;
   margin-bottom: -25px;
 }
 
 .panel-arrowcontent {
   -moz-appearance: none;
   background: var(--arrowpanel-background);
-  border-radius: var(--arrowpanel-border-radius);
   box-shadow: 0 0 0 1px var(--arrowpanel-border-color);
   color: var(--arrowpanel-color);
   border: none;
   padding: var(--arrowpanel-padding);
   margin: 1px;
 }
 
 .panel-arrow[side="top"] {

--- a/toolkit/themes/windows/global/popup.css
+++ b/toolkit/themes/windows/global/popup.css
@@ -52,26 +52,16 @@ panel[type="arrow"][side="right"] {
   color: var(--arrowpanel-color);
   background: var(--arrowpanel-background);
   background-clip: padding-box;
   border: 1px solid var(--arrowpanel-border-color);
   box-shadow: 0 0 4px hsla(0,0%,0%,.2);
   margin: 4px;
 }
 
-%ifdef XP_WIN
-@media (-moz-os-version: windows-win7) {
-%endif
-.panel-arrowcontent {
-  border-radius: 4px;
-}
-%ifdef XP_WIN
-}
-%endif
-
 .panel-arrow[side="top"],
 .panel-arrow[side="bottom"] {
   list-style-image: var(--panel-arrow-image-vertical,
                         url("chrome://global/skin/arrow/panelarrow-vertical-themed.svg"));
   position: relative;
   margin-left: 10px;
   margin-right: 10px;
 }