X-Notifier not working

Assuming X-notifier is still installed (Tools->Add-ons):
1. Right-click the Menu Bar (or View->Toolbars)
2. Choose Customize...
3. From there you can drag the X-notifier icon to where you want it
4. and elect to show the X-notifier toolbar (also thru View->Toolbars)

Notifier has not been checking mail.com in google chrome for the past few days.

Same here, various accounts will be checked and various not.

A little bit freaky, but 2 gmail accounts are checked and another 2 will not. Also not gmx.com and gmx.de

Any solutions?

Try to reinstall, delete cache and cookies, delete and reinstall the accounts and scripts...

EDIT

After log off/log in in  my google accounts, they work again.

But gmx.com and gmx.de does not work anymore...

Mail.com is still not being checked.