I've been using this extension for, I don't know, how many years. At least 5, but probably more, and I love it.
There are a couple of things that this extension is missing on Firefox, though.
1. Shortcuts. Chrome's version has the ability to set activation hotkeys and some more. That's not the case for Firefox. As one of the many users who prefer keyboard-driven workflow, this feature is really missing. In fact, this is the only extension (out of 10) that forces me to use a mouse. I hope this feature will be added.
2. Auto dark mode. I can manually set the dark theme, but It would be nice if the extension could follow the system theme.
Other than that, the extension is really must-have.

I've been using this extension for years, always been happy with is.

One feature request: I would like to have the ability to have an email account added, but for it not to include emails from that account added in the little red number. (I have my wife's email accounts added on the desktop, but I don't need a running tally of how many emails she has unread, and I don't want to be bothering her and telling her to clean out her email accounts.)

I have been using this add-on for close to one year now and it has been a lifesaver when I am waiting for a reply knowing when it arrives. EXCELLENT! Highly recommended.

I just realized I've been using this addon since 2011? 2012? It's been a massive amount of time, and it's still one of the first I install when setting up a new browser.

I can't recall ever having an issue, it's rock solid and works perfectly for how I use email.

I monitor 9 diff. email addresses from Checker Plus. Nothing better.

works well enough for checking emails, but is really lacking a keyboard shortcut to open the preview window without having to click on it

Unobtrusive and easy to use, this add-on has really helped me be more mindful of my messages. I'm easily distracted and the fact that there is a built-in reminder via the 'Repeat Notification' function is wonderful. The UI is easy to navigate and the customization options are near endless, so you can easily match Checker to any other themes you might be using. The only problem I ran into was with upgrading (which was entirely on my end), so I reached out about it and got a super fast feedback message from Jason that sorted things out immediately (Thanks again for that!)

I'd 100% recommend this add-on to anyone, but especially to people like me that are more accustomed to Discord and Steam style desktop message notifications and looking for a similar interface.

Nice UI, wonderful functional. Like it very much

I really like being able to right click on tabs and email them, but the notification function keeps disabling itself. If/when I notice that, I have to go in and wake the hamster running the process.