clipped from: How to Manage Firefox Tabs better
Ok I'll try to be short. When you open many tabs(more then 8-10 tabs) in Firefox, the "close button" disappears . This was made to look good but at least for me it's annoying because i need first to click on the target tab in order to see it and then close it.
You can set in Firefox to see the whole tab when there are many. Here is how.
1. Type in the navigation bar: about:config
2. Next search for the lines from the picture and modify them as you see there.
Tip:Double click on the line to change it.
3. Restart Firefox for changes to take effect. Now each tab will be visible and you'll be able to close it in 1 click.