Do you have the Firebug add-on? Some versions of that add-on caused 2 title bars to appear. If you have Firebug try updating to the latest version.

If you do not have Firebug, check to see if another add-on is causing this. For details of how to do that see https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

I uninstalled firebug some days ago but it made no difference.

sorry, but I have better things to do than going thru troubleshooting steps. FF3 never worked well for me because of those insane memory leaks, looks like FF4 is a step backwards.

I had this problem, but I found it to be the Google Toolbar plugin. That is now disabled, and all is working great again.

firefox is the problem, not google toolbar. I went back to IE on that computer and everything works great, no more memory leaks, speed issues, crashes, double windows.

FF used to be the best browser at one point, but this is history.

I have this problem too, and do not have Firebug installed. It only happens when I open a second window. On the second window, the link for add-ons doesn't work. There is definitely a serious problem with Firefox 4. Chrome, IE or Opera are starting to look like attractive alternatives.

yeah, I switched to IE and I am not looking back. On I am only missing a working addblock, that is all.

Phew - I found by disabling Babelfish, most of my problems went away. Mystery - I also had to disable Roboform Toolbar 7.2.5, but find that Roboform still works! I am now a happy bunny and delighted to be back using FF again.

hmm, I also have roboform, I will try to disable it

I spent ages debugging this issue and found that the following addons caused issues for me....

XMarks 4.0.2 Firebug 1.8.3

By the way, Roboform (7.4.1) was fine.

I have disabled them for now and all good. Will try updating and googleing further from now.

Was firebug for me, even though I'm using the newest version (1.8.4), released early November 2011. maybe they re-introduced the problem. Grrrr. What a big hassle. Looks like the built-in FF web developer tools have come a long way and Firebug is going to get the boot (too memory intensive anyhow)