If you are using Tab Mix Plus then check its options.

I don't know what Tab Mix Plus is so that must not be the problem.

You can check this pref on the about:config page: http://kb.mozillazine.org/browser.tabs.closeButtons

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.

Followed your directions. It's set to 1. I changed it and restarted Firefox with no change in the problem. Reset it to 1 and still no change. Before this upgrade there was no problem with the X showing on the tabs. Now I have to right click on the tab to close it.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

You can also try "Reset all user preferences to Firefox defaults" on the Safe mode start window - See http://kb.mozillazine.org/Resetting_preferences

(the MozillaZine KB is currently down, so you may need to try again later)

Same problem :(

Same answer, either install an extension that has that pref or set it through about:config

This cal also be a problem with a theme (Walnut), so make sure that all extensions and themes are updated to the latest versions.

I checked the about:config setting and I upgraded the Wallnut theme and still no change.

Haven't tried the suggested fixes & my version of Firefox is 3.5.3 instead of 3.6.3, but I have the same problem.

I had the home page set to "about:blank" when I noticed that the x was missing. I then clicked on "Restore to Default", restarted and then selected "Show a blank page" - Restarted again and this time it worked, except that there is no x when there is only one tab. As soon as a second tab opens, an x suddenly appears on all the tabs. Keep in mind that I also updated the Walnut theme and all other add-ons. Not entirely happy with this niggle, but I can live with it. Version 3.6.3 is faster and that makes up for it.