--- a/devtools/client/responsive.html/browser/swap.js
+++ b/devtools/client/responsive.html/browser/swap.js
@@ -59,16 +59,23 @@ function swapToInnerBrowser({ tab, conta
 
       // 1. Create a temporary, hidden tab to load the tool UI.
       let containerTab = gBrowser.addTab(containerURL, {
         skipAnimation: true,
       });
       gBrowser.hideTab(containerTab);
       let containerBrowser = containerTab.linkedBrowser;
 
+      // Copy tab listener state flags to container tab.  Each tab gets its own tab
+      // listener and state flags which cache document loading progress.  The state flags
+      // are checked when switching tabs to update the browser UI.  The later step of
+      // `swapBrowsersAndCloseOther` will fold the state back into the main tab.
+      let stateFlags = gBrowser._tabListeners.get(tab).mStateFlags;
+      gBrowser._tabListeners.get(containerTab).mStateFlags = stateFlags;
+
       // 2. Mark the tool tab browser's docshell as active so the viewport frame
       //    is created eagerly and will be ready to swap.
       // This line is crucial when the tool UI is loaded into a background tab.
       // Without it, the viewport browser's frame is created lazily, leading to
       // a multi-second delay before it would be possible to `swapFrameLoaders`.
       // Even worse than the delay, there appears to be no obvious event fired
       // after the frame is set lazily, so it's unclear how to know that work
       // has finished.
@@ -142,16 +149,21 @@ function swapToInnerBrowser({ tab, conta
 
       // 4. Swap tab content from the browser within the viewport in the tool UI
       //    to the regular browser tab, preserving all state via
       //    `gBrowser._swapBrowserDocShells`.
       dispatchDevToolsBrowserSwap(innerBrowser, contentBrowser);
       gBrowser._swapBrowserDocShells(contentTab, innerBrowser);
       innerBrowser = null;
 
+      // Copy tab listener state flags to content tab.  See similar comment in `start`
+      // above for more details.
+      let stateFlags = gBrowser._tabListeners.get(tab).mStateFlags;
+      gBrowser._tabListeners.get(contentTab).mStateFlags = stateFlags;
+
       // 5. Force the original browser tab to be remote since web content is
       //    loaded in the child process, and we're about to swap the content
       //    into this tab.
       gBrowser.updateBrowserRemoteness(tab.linkedBrowser, true, {
         remoteType: contentBrowser.remoteType,
       });
 
       // 6. Swap the content into the original browser tab and close the