Weird Firefox lock-up bug

This is the third time this has happened to me, always on QT3, so I think it’s related.
Firefox 1.5
When I go to click on a thread from the forum page (or maybe it only happens when I click for a specific page?) the Firefox window stops responding. Some of the menus still kind of work, you can open them and their submenus, but you can’t choose any options. You can still select text on the page, and when you click a link you get the box around it, but nothing happens. The status bar says “Transferring data from…” The whole window is dead, including the other tabs. I don’t have any other Firefox windows open so I don’t know if it happens with them, too.

I am having the same problems with the latest Netscape too. For a week or so now. I don’t know what is causing it.