You should see a pop-up block icon in the right corner of the Status Bar if you have chosen to hide the information bar at the top.

You can left-click that pop-up block icon on the Status Bar and remove the check mark from "Don't show info message when pop-ups are blocked".

You can look at these prefs on the about:config page and reset them via the right-click context menu:

Status bar icon: browser.popups.showPopupBlocker
Info bar at the top: privacy.popups.showBrowserMessage

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.
You can use the Filter bar at to top of the about:config page to locate a pref more easily.

There is no longer a status-bar; where is the pop-up block icon now? thx

You can find the pop-up block icon on the right end of the location bar.

Sorry, still can't find pop-up block icon; the icons on right end of my location bar are:

• "bookmark this page" and
• "reload current page";

I am running Firefox 8.0. thx, bob

You only get that icon if pop-ups are disabled and there is a pop-up blocked.

• http://www.popuptest.com/popuptest1.html