--- a/browser/components/extensions/ext-utils.js
+++ b/browser/components/extensions/ext-utils.js
@@ -483,21 +483,22 @@ class ViewPopup extends BasePopup {
         bottom: Math.max(0, screenBottom - popupBottom),
         top:  Math.max(0, popupTop - win.screen.availTop),
       };
 
       // Create a new browser in the real popup.
       let browser = this.browser;
       yield this.createBrowser(this.viewNode);
 
+      this.ignoreResizes = false;
+
       this.browser.swapDocShells(browser);
       this.destroyBrowser(browser);
 
-      this.ignoreResizes = false;
-      if (this.dimensions) {
+      if (this.dimensions && !this.fixedWidth) {
         this.resizeBrowser(this.dimensions);
       }
 
       this.tempPanel.remove();
       this.tempPanel = null;
 
       this.shown = true;