How to Unsubscribe from Browser Notifications

Chrome Notifications Tom's Hardware Firefox
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If you're on Google Chrome

If you're in Google Chrome, go to Settings > Advanced > Content Settings > Notifications

From there, check to see if you have notifications from Tom's Hardware in the 'Allow' list. Tom's Guide has one as well, and they look like this:

From there, just hit the option list next to it, select 'block' and it will appear on the Block List in your Notifications settings.

If You're Using Firefox

From Firefox, go to Options > Content, and check the Notifications Section. Click the 'Choose' Button to see which sites you have allowed or blocked notifications from. From there you can remove the sites that you have blocked/allowed notifications, and the next time you visit that site it will ask again for permissions to send you notifications.

There's a 'Do Not Disturb' Option on Firefox, but it only stops new notifications from popping up until you restart the browser.