Why does a window still open even though blocking is on?

Because most blockers allow windows tied to a direct user click. A page can wrap its pop-up in a click handler and slip past the check.

How do I let one trusted site open a window without turning blocking off?

Add that single site to the allow-list. The main switch stays on and every other site remains blocked.

Is it safe to click Allow on a pop-up that appeared by itself?

No, not without checking the address first. Some script-opened pop-ups carry a secondary payload that uses cross-site scripting.

Do mobile browsers need the same procedure?

Yes, the same settings path applies, though the menu labels differ. Open the browser menu, find privacy or site settings, and set pop-ups to blocked.

44%click-through of the first AT&T banner on HotWired

70%share of 2016 US digital ad revenue held by two companies

90%yearly growth of US mobile ad spend, 2010 to 2013

44%First banner click-through

Block them in five steps

Adwall — Pop-Up Ads and Browser Blockers | adwall.net

Pop-up ads appear because a script on a page calls a window-opening command, and browsers ship with a blocking switch that most users never turn on. This page gives the ordered procedure, the dated milestones of built-in blockers, and the checks that tell a script-opened window from a legitimate one.

adwall.net
How pop-ups open and how blockers stop them
Ordered steps, dated milestones, and the reasons pop-ups still get through

Ordered index

Index

44%First banner click-throughThe first AT&T banner ad on HotWired had a 44% click-through rate.

70%Two-company revenue shareGoogle and Facebook were estimated to be responsible for 70% of overall US digital advertising revenue in 2016.

90%Annual mobile ad growthUS mobile advertising spending grew about 90% each year from 2010 to 2013.

Numbers and dates at a glance

Dated and numeric milestones behind pop-up advertising and its blockers
What happened	When or how much	Where it applies
First AT&T banner on HotWired, click-through	44%	Banner format on a single page
Pop-up ads first appear	Late 1990s	Tripod.com webpage hosting site
Mozilla pop-up blocker released	23 September 2002	Mozilla browser
Opera pop-up blocker released	13 November 2002	Opera browser
Windows XP SP2 adds blocking to Internet Explorer	2004	Internet Explorer on Windows XP
Two companies' share of US digital ad revenue	70% in 2016	United States digital advertising
US mobile ad spend yearly growth	about 90% per year, 2010–2013	United States mobile advertising
Internet ad revenue vs cable and broadcast TV	Surpassed in 2016	United States advertising market

Dated and numeric milestones behind pop-up advertising and its blockers

How a pop-up reaches your browser

A page script calls a window-opening command and the browser decides whether to honor it.

Pop-up ads originated on the Tripod.com webpage hosting site in the late 1990s. The hosting pages carried scripts that opened a second window on top of the page a visitor was reading, and the pattern spread from there.

The browser receives the open-window request, checks its blocking setting, and either renders the window or swallows the request. When blocking is off, the window opens immediately; when blocking is on, the request is discarded unless the site sits on the allow-list.

A window opened by a click is treated differently from one opened by a background script. Most blockers allow the first and stop the second, which is why the procedure below starts with the settings switch rather than with page-level workarounds.

Click-opened windows are generally allowed by default blockers.
Script-opened windows are the class that blocking settings target.
Allow-listed sites bypass the block even when the main switch is on.

Terms in the blocking panel

Pop-up ad: An advertisement shown in a second browser window opened by a script rather than by the page the visitor is reading. The format originated on Tripod.com in the late 1990s.
Pop-up blocker: A built-in browser setting that discards window-opening requests not tied to a direct user click. Mozilla shipped one on 23 September 2002.
Allow-list: A per-site exception list that lets named sites open windows even when the main blocking switch is on. Entries persist until removed by hand.
Cross-site scripting (XSS): A technique that runs script in a page context the attacker does not own. Some script-opened pop-ups carry a secondary payload that uses it.
Click-through rate: The share of impressions that result in a click. The first AT&T banner ad on HotWired had a 44% click-through rate.

Questions visitors actually ask

Why does a window still open even though blocking is on?: Because most blockers allow windows tied to a direct user click. A page can wrap its pop-up in a click handler and slip past the check.
How do I let one trusted site open a window without turning blocking off?: Add that single site to the allow-list. The main switch stays on and every other site remains blocked.
Is it safe to click Allow on a pop-up that appeared by itself?: No, not without checking the address first. Some script-opened pop-ups carry a secondary payload that uses cross-site scripting.
Do mobile browsers need the same procedure?: Yes, the same settings path applies, though the menu labels differ. Open the browser menu, find privacy or site settings, and set pop-ups to blocked.

How this page was assembled

The procedure follows the settings path shared by mainstream desktop and mobile browsers. Dates and percentages are taken only from the documented release and market records listed below. Nothing on this page is quoted from a vendor or a company holding this domain.

Sources

Release dates, click-through figures, and market shares come from the documented records cited in the table above.