Looking FireFox code

While looking FireFox code in the file

tabbrowser.xml

line 1727
i found the function "SwapBrowserAndCloseOther".

From what I can see these lines
1742 var ourIndex = aOurTab._tPos;
1743 const filter = this.mTabFilters[ourIndex];
1744 var tabListener = this.mTabListeners[ourIndex];
1745 var ourBrowser = this.getBrowserForTab(aOurTab);
1746 ourBrowser.webProgress.removeProgressListener(filter);
1747 filter.removeProgressListener(tabListener);
1748 var tabListenerBlank = tabListener.mBlank;

stop the tab a browser processes

while this line hooks the tabs processes to the new browser

ourBrowser.swapDocShells(aOtherTab.linkedBrowser);

Now for the long process of figuring out how these functions work