I think you can fix your problem by Click-right mouse on top your browser > Custom...> Drap & Drop buttons Previous-Next. OR maybe Firefox 4.0 beta 1 isn't stable. You should install Firefox version 3.6.6 Good Luck !!!

The XPCOM components registration has been changed in the yesterday's nightly build and that has caused a lot of extensions that register XPCOM components to get broken. See http://forums.mozillazine.org/viewtopic.php?f=23&t=1937639

Thank you both for taking the time to reply. I also thought it had something to do with changes from mozilla. In the meantime I have changed to 3.6.6, as titixuxu suggested, and it works great! I am hoping they fix the issue really soon.

I was having the same issue and titixuxu's post helped me stumble upon the solution.

Right click the main (navigation) toolbar and click customize.

Here's the trick...buttons in the customize window can be placed in ANY toolbar now, including the bookmark and tab toolbar.

Place the "new tab" button at the end of the tabs toolbar. It won't look quite right at first, but click "done" and voila! There's the new tab button you're looking for.

Be warned that a button can only be placed once... so if it's already in your navigation toolbar, you might have to drag it from there to the tab toolbar where it now belongs.

That's what I had to do, since I installed this on top of 3.6, and it copied my customizations over, including the tab button I had added to the old nav toolbar.

Kyle, thank you for your reply. I have managed to fix it using your instructions, although now I don't have the button on my navigation bar, which is a little confusing to me (I've always had it there since firefox version 1).

I hope they'll make an extension for that :)

Thank you all for your replies

how do I get back to the previous version?

I'm going to make a Firefox addon that allows me to have a "New Tab" button in both the navigation bar and in the tabs bar, at the same time. I shall upload it to the Mozilla Firefox Addons Repository.

This new functionality has already existed in an earlier version of Firefox, Firefox 3. Unfortunately it has been removed from Firefox 4, leaving me as an unsatisfied user. I hope my new addon will remedy that.

I also miss the status bar a lot.

Edit: (I also want my "Back" and "Forward" buttons to be separate. I would like to place my "Reload / Stop" button between them. They broke that in Firefox 3. There was an addon that fixes it, but it was of poor quality and neglected by it's author, the last time I checked.)

/  :(

You probably only need to use some code in userChrome.css to make the New Tab button on the Tab bar visible

#new-tab-button {visibility:visible!important}
.tabs-newtab-button{visibility:visible!important}

• Status-4-Evar: https://addons.mozilla.org/firefox/addon/235283/
• Go classic: https://addons.mozilla.org/firefox/addon/13129/

I found the new tab button! It was in the tab bar, which is hidden when you only have one tab open, farthest to the right. If you have two or more tabs open, you will see two new tab buttons, one directly after the tabs, and our missing friend to the right. He looks a little thorn, just a barely noticeable [+] sign.

To get it back into the navigation bar, right-click on the navigation bar, choose customize, drag the new tab button from the tab bar to the navigation bar, and the button will change its appearance back to normal.

Thanks luff. I knew about going into customize and dragging, but whenever I dragged it, the button appeared on the right. So I would cancel it.

What actually happens is you drag it to the tab bar and it will snap all the way to the right, but when you click "done" it will pop back next to the tabs.

This discussion is on 4.0 and its not there.

I have this in the userChrome.css.

Doesn't work, mate.

I see no new tab button. When I customize, I see no "New Tab" button as a possibility there either. It used to be there and was draggable to the toolbar.

This is seriously the most stupid thing Mozilla has done in recent years. It's fine to improve UIs. But don't change it forcefully in a way that users, who get accustomed to doing things a certain way, have to relearn everything and struggle.