How is this being displayed, a pop-up?

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no, its more of a "redirect" of the browser to a subscribe page when I click on an article. added the adblcok, but no success. again...both major newspapers in my area Balt/Wash seem to allow the windows browser but go immediately to the redirect to subscribe page with firefox.....

Please post the links you were trying to use.

Are you blocking cookies? Often sites remember that they already annoyed you with an overlay or interstitial page by setting a cookie so they don't do it again and again.

This article describes how to set Firefox cookie preferences for maximum compatibility: Websites say cookies are blocked - Unblock them

If you are using the new tracking protection feature, that also might be a factor -- not enough tracking! See: What happened to Tracking Protection?

For me the Washington Post website allows 5 "free" article views per day and then it asks me to sign-in or subscribe. Never read the Baltimore Sun.

It seems likely this is not a Firefox issue, but rather you are running up against a paywall.

• https://wikipedia.org/wiki/Paywall