You will need to install a user script manager extension to install this script.
Since GOG.com doesn't offer any kind of e-mail notification for forum updates, this extension allows you leave your favourite threads list open in a tab and use it as an update monitor.
This has three benefits:
As GOG notifications have been known to not update immediately in the past, an "Ignore Stuck Notification Count" command is provided under the "User Script Commands" submenu, which operates as follows:
Users of Greasemonkey 4 can find the "Ignore Stuck Notification Count" option in the page's context menu.
While the most recent release is currently only tested on Greasemonkey 4, it uses the polyfill for supporting the older APIs and has only been changed minimally from previous versions which were tested on Firefox under Greasemonkey 3 and Chrome under Tampermonkey.