Works great.

Ho provato quasi tutti i notifier di email presenti nella sezione Add-On di Firefox e Chrome, ma questo è decisamente il migliore.
Lettura, scrittura ed eliminazione delle email rapida, supporta più di un account contemporaneamente e non si blocca. Consigliato!

C'est un excellent addons. Les lenteurs que j'avais pu constater il y a quelques jours ne sont dues qu'à Gmail qui ralentit ou bloque Firefox pour nous obliger à utiliser Chrome.
Au contraire, en consultant ses mails à l'aide de Checker plus, ça reste relativement fluide, et en tous cas, ça ne bloque pas.
Cet addon serait bienvenu sur Palemoon et sur Brave

There was another review saying it doesn't automatically check for updates in FF 57, so I'm just living a review to say that it does work for me.

I've only been using this plugin a few hours in FF, but I used it for years in Chrome, so very happy to give the 5 star review.

Very useful, best addon for gmail.

Finally, found best gmail checker extension (tested on 55.0.2 64 bit)

ATM, this is the best WebExtensions Gmail checker/button. The built-in popup isn't annoying and if you really want just a button and notifier to Gmail you can just choose so.

By default this is broken in Fx57 though, because Tracking Protection enabled seems to inhibit the addon from logging in. Not sure if this is a Firefox or addon bug.

Checking it now

A lot of reviews are probably from competitors since this is the best one I've used and I've used them all.

Love you
More power

After using another much more rudimentary add on, this well written and continually updated add on is a pleasure to use.
Don't feel the need to go into specifics as it's all in the description, suffice it to say if you use Firefox and Gmail this is a must have add on.

I have used the Gmail Checker before, but now it is broken by changed in authentication process. I have installed this app and I really comfortable with it - i find the opening pop-up windows where you can manage your accounts and mails is really super!

The best extension I have ever used to manage Gmail accounts.
Five stars for sure!

This was the ultimate mail checker extension on Chrome and now that I've switched to Firefox, I'm very pleased to see that it's available here, too. However it doesn't work on Firefox 53 it appears. After setting up everything as usual, the icon shows an x in the upper corner and is greyed out. I can't even open the settings anymore. I only get an endless loading icon…

I have just switched over from Chrome to Firefox, and to my utter delight, I found out that Checker Plus is available for Firefox as well!

This extension is a must-have extension for anyone who uses Gmail to any degree. THe extension is intuitive, the layout/UI is efficient, and it is very hard to use a browser without it once you get used to it.

Of equally great import - the developed, Jason, is a thorough professional. If you have any trouble with his extension, be sure to email him or to leave your email address when you remove the extension from your browser. He WILL get back to you promptly, and he WILL fix your problem promptly.

Very Good! It fllow me from Chrome to Firefox. I it the best in same type plugins.