How to keep Firefox 3.5 running after closing last tab and add a close tab button on the last tab
Firefox 3.5 came with one one more annoying UI change that is once you have closed all the other tabs and only one tab is open the close tab button disappears from the tab and you can now just close the Firefox window by pressing the close button on top right or just hit ctrl+w but the problem is that this behaviour is not really suitable for a browser like Firefox which takes ages to start once you close it unlike Google chrome, and personally i am used to closing all the stuff in the tabs and let Firefox keep running and then open any website i have to in the empty tab. so now i am going to show you guys how to disable Firefox from closing the window when you close the last tab.
Type about:config in your Firefox address bar and press enter press the “I’ll be careful, I promise!” button and now search for “browser.tabs.closeWindowWithLastTab” and double click it to change its value to false, now whenever you close the last tab using ctrl+w or the close tab button we are just going to add the Firefox window wont close.
How to remove the new tab button in Firefox 3.5
Mozilla Released Firefox 3.5 a while ago and as always there were some UI changes and if you are like me and don’t like getting used to new stuff again and again you definitely 
wont like these useless changes , one such change is the addition of the new tab button which is totally useless for me and just occupies valuable space on my tab bar 
as I use double click (on the tab bar) to open new tabs so i just removed it, i will show you guys how to remove it.
Removing it is pretty easy without harming anything, we are going to use the userChrome.css file to edit the layout of Firefox don’t worry it only sounds dangerous but it isn’t 
in fact this file is used for creating themes for Firefox.
ok now lets do it, at first we need to open the chrome folder where the userChrome.css file resides for that you need to browse to “x:\\Document and Setting\%your username%\application data\Mozilla\Firefox\profiles\%your active profile folder%\chrome\” (where x is your windows installation directory), once you are there, you have to find the userChrome.css file if its not there, don’t worry, its not there for most people just open userChrome-example.css file and save it as userChrome.css and now add these lines to it under the @namespace line:
/* remove New Tab button */
.tabs-newtab-button {display:none !important;}
Once you are done with adding those lines just save the file and restart Firefox and now the new tab button will be gone, if it is still there then there must have been some problem, just leave a comment and i will be glad to help you out.
