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 it looks like this: https/tomsguide.os.tc:443
From there, just hit the option list next to it, select 'block' and it will appear on the Block List in your Notifications settings.
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.