Add an omission of isFF logic to avoid no changes after run in other browsers.

[NatalieXSelina]

I'm an outreachy candidate, and trying to understand the project. I'm interested in both the Tor browser and the TZP project, and I find that they both require some knowledge of the FireFox browser, so I'm still working on that. I've only made one tiny contribution so far, and I had to submit it due to Outreachy's deadline. But I will continue to try to contribute to the project by diving into and completing some of the Tasks mentioned in Issues.

[Thorin-Oakenpants]

This is an old test that is not applicable anymore. Here's how I would fix it

there is no dom element called isFF, it is a global variable. And I wouldn't put it in the outputAppLanguage() function. Instead I would automatically display it (that's promising get_globals() and then display the text) , and then I would stop anything happening (like clearing the results) when the user clicks run - that's the rerunAppLanguage() function

If you want to amend your PR, then I can commit it

function rerunAppLanguage() {
    if (!isFF) {
        return
    }
    // clear
    let items = document.getElementsByClassName("c")
    for(let i=0; i < items.length; i++) {
        items[i].innerHTML = "&nbsp"
    }
    // pause so users see change
    setTimeout(function() {
        outputAppLanguage()
    }, 170)
}

Promise.all([
    get_globals()
]).then(function(){
    if (!isFF) {
        dom.appLang1.innerHTML = "this test requires "+ s4 + "GECKO" + sc +" ... and you're not it"
    }
})

[NatalieXSelina]

Oh, thanks for the suggestion, I will amend my PR