If you have Windows, press and hold down the Ctrl and Alt keys, then press and release the Delete key.
This should give you the Windows Task Manager.

Click on the Applications tab and see if there are any that look like they’re related to the pop-ups.
If you see an application that looks like a pop-up generator, click on it, and then click on the End Task button at the bottom of the Manager.
I.e., if you see a task that doesn’t look like something that you want to be running, end it.

I don’t know about the other browsers, but Mozilla Firefox with Add Block Plus, rarely if ever allows any pop-ups.