This method also stopped working at some point, possibly with 29 (Australis) or 57 (Photon) UI. I am not aware of any alternative at the moment.
You can navigate to about:config
and set the value browser.tabs.tabClipWidth
to 1
. You will need to restart the browser.
As others have suggested, the close tab button is removed if the tab becomes too small (narrow). This setting determines the minimum width of the tab in pixels below which the close tab button is not shown (140
is default). Setting it to 1
essentially means always show the close tab button, no matter how narrow the tab is. According to the linked article, 0
is not a valid number (but the button is 16 px anyway).
This setting has an effect in all versions of Firefox from 1.6a1 onwards (confirmed working in 13.0.1).
As of Firefox 23.0, this method no longer seems to work. They may fix it in a future update to the extension, so I will leave it here for now. The config option described above is still available.
An alternative (and the one that I am using) is the Tab Mix Plus extension. This extension includes many other possibly (un)desired features, and obviously isn't as clean as the setting above, but it is what I've been using (for other reasons, the close button was just a side effect).
In TMP's options, Display
> Tab
> Close tab button
> on all
.
Click for full size
Wilson's answer links to an extension that is no longer available. Both the config and TMP setting described in this answer achieve the same effect.
I don't know how to do it exactly as you request. I'm unsure if we can reuse an existing tab when typing in an address if it happens to be on the same domain of an opened tab.
However, Closy allows you to close duplicate tabs, while TabCloser allows you to close tabs with the same domain name.
Best Answer
Try the "split browser extension".