Firebird Question

Im sure this can be summed up in a sentence, and it is a stupid question for me to ask, but ill ask anyway.

Sometimes when im running Firebird(mozilla) ill come across a site where i want to open a window, or click a link that opens up. But i notice in the bottom left hand corner, a dark blue cirlc appears, almost like a pool ball.

After this appears, im unable to open a pop up window, such as a reply window, or something to that degree.

If i refresh sometimes, it will go away.

Anyone mind explaining to me what causes this?

Its prolly caused by the popup blocker thats bundled with firebird/firefox(depending on the version you are running). You can allow some sites or disable it all together in the tools->options menu under 'Web Features'.