"open in background tab" behaves different from "open link in new tab" from the context menu about foxygestures

[Aran-Fey]

I made this userscript as a workaround:

const url = data.element && data.element.linkHref;
if (url){
    executeInBackground(async (url) => {
        // If this is the first time this script is executed, initialize some stuff
        if (window._lastOpenedTabId === undefined){
            window._lastOpenedTabId = new Map();
            window._successorTabId = new Map();
            
            // When a tab is closed, activate the next one
            browser.tabs.onRemoved.addListener(function(tabId){
                if (!window._successorTabId.has(tabId)){
                    return;
                }
                
                const successorTabId = window._successorTabId.get(tabId);
                browser.tabs.update(successorTabId, {active: true});
            });
        }
        
        const openerTab = (await browser.tabs.query({active: true}))[0];
        const lastOpenedTabId = window._lastOpenedTabId.get(openerTab.id);
        
        let newTabIndex = openerTab.index + 1;
        if (lastOpenedTabId !== undefined){
            try {
                const lastOpenedTab = await browser.tabs.get(lastOpenedTabId);
                newTabIndex = lastOpenedTab.index + 1;
            } catch (error){
                // That tab has been closed
            }
        }
        
        const newTab = await browser.tabs.create({
            url: url,
            active: false,
            index: newTabIndex,
            openerTabId: openerTab.id,
        });
        
        window._lastOpenedTabId.set(openerTab.id, newTab.id);
        if (lastOpenedTabId !== undefined){
            window._successorTabId.set(lastOpenedTabId, newTab.id);
        }
    }, [url]);
}