Firefox 1.0 Preview Release popup-blocker problem
Note: This problem does not seem to affect FF1.0 on Windows XP Pro...and I don't know about other Windows flavors, but it happens here on Linux, and a very similar problem manifests the Mac, but apparently not exactly the same problem.

The problem here is:
After 20 popups (the default dom.popup_maximum setting) from a site which pop up something containing an onclick or onmouseover and onmouseout, popups are blocked from the site until restart of browser. This is true (as someone else noted on bugzilla) even if you don't have "Block Popup Windows" checked in the preferences.

In other words, I believe that when FF1.0-Linux manages it's count of currently open popups from a site, it fails to un-count them when you close them if they had contained any onclick or onmouseover events.

Below is the simplest test case. Two links, both open a new window. The first link opens a copy of this document that you're now viewing, but with a simple link at the bottom and no onclicks or onmouseovers. The second opens an exact copy of this page. Because this document contains "onclick", "onmouseover" and "onmouseout" on the links below, I can only open the second link x times before all further popups are blocked.

Test OK - version of this page which lacks these links at the bottom.

Test Bad - link to exact copy of this page, with bottom links.