Restart Button for Firefox. An updated version of https://github.com/Endor8/userChrome.js/tree/master/restartfirefoxbutton_movable. Middle click also empties the script cache.

RestartFirefoxButton_Movable.uc.js

(function() {
    if (location != 'chrome://browser/content/browser.xul' && location != 'chrome://browser/content/browser.xhtml')
        return;

    try {
        CustomizableUI.createWidget({
            id: 'restart-button',
            type: 'custom',
            defaultArea: CustomizableUI.AREA_NAVBAR,
                onBuild: function(aDocument) {
                    var toolbaritem = aDocument.createElementNS('http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul', 'toolbarbutton');
                    toolbaritem.onclick = event => onClick(event);
                    var props = {
                        id: 'restart-button',
                        class: 'toolbarbutton-1 chromeclass-toolbar-additional',
                        label: 'Restart',
                        tooltiptext: 'Restart (with middle click userChrome.js cache is emptied)',
                                    style: 'list-style-image: url(chrome://browser/skin/sync.svg)'
                    };
                    for(var p in props)
                        toolbaritem.setAttribute(p, props[p]);
                    return toolbaritem;
                }
        });
    } catch(e) {};

    function onClick(event) {
        if(event.button == 1)
            Services.appinfo.invalidateCachesOnRestart();
        else if(event.button == 2) 
            return;

        let cancelQuit = Cc["@mozilla.org/supports-PRBool;1"].createInstance(Ci.nsISupportsPRBool);
        Services.obs.notifyObservers(cancelQuit, "quit-application-requested", "restart");
        if(!cancelQuit.data) 
            Services.startup.quit(Services.startup.eAttemptQuit | Services.startup.eRestart);
    }
})();

Save config.js to Firefox installation folder, next to firefox.exe
Save config-prefs.js into \defaults\pref inside Firefox installation folder, next to channel-prefs.js
Save userChrome.js into Firefox chrome folder, next to userChrome.css
and it works

and it works

Yes - yes, it does :-) Thanks for the help, @rpolo77 and @you74674.

The solution provided by you74674, and the instructions from rpolo77, works great on Windows. I tried saving the same files in the equivalent locations (hopefully) on my Linux MInt system, but it doesn't work. Either I have something wrong, or this just won't work on Linux. Any thoughts? I'm guessing the problem(s) may be within the .js files themselves, but I'm not strong on that kind of work.

config.js is in /usr/lib/firefox, next to firefox.sh
config-prefs.js in /usr/lib/firefox/defaults/pref, next to channel-prefs.js
userChrome.js in /home/ken/.mozilla/firefox/[profile].default/chrome, next to userChrome.css

Restart restored, thank you all so much. I had upgraded to 78.3esr and it broke userchrome and the restart button.

Tabs on the top again, those ba****rds!!!

@rpolo77 and @you74674

Firefox 82.02

I followed the instructions.

Save config.js to Firefox installation folder, next to firefox.exe
Save config-prefs.js into \defaults\pref inside Firefox installation folder, next to channel-prefs.js
Save userChrome.js into Firefox chrome folder, next to userChrome.css
and it works

Also moved RestartFirefoxButton_Movable.uc.js to the chrome folder, but the button does not appear.

Is this still supposed to work, or am I missing something? Can someone post what the button looks like?

Did you go to Customize and add the button to your toolbar area?

Button looks like this: https://prnt.sc/vdnwr0

Guess what? I didn't have RestartFirefoxButton_Movable.uc.js in the Chrome folder after all. Dumb.

So happy. Works fine. Been hoping to find this type of restart option for a long time now.

In past custom button setups, it was possible to source the button image from a local file. I still have the previous RestartFirefoxButton_Movable.uc.js. The section of that file pertaning to the button starts with

var dataUrl = "data:image/png;base64," +

after which the base 64 code is added.

Can someone tell me if this can be done, and if so, how?

Thanks

I just upgraded to Firefox 89, and the restart button icon changed

Firefox 88.01

Firefox 89

Is there a way to bring it back?

It doesn't work :(