There are probably extensions that allow to do that, however, this is not necessary as I will show in this post. Maybe you’ve seen the functionality in Safari or just wondered why the close button for tabs in Firefox can’t just always be there. In Safari, the close button appears when hovering over the tab itself.
The following modification adds this functionality to Firefox. You need to create a file called userChrome.css
with the following content:
Firefox v113 and later
.tabbrowser-tab:not([selected]):not([pinned]):hover .tab-close-button {
display: flex !important;
}
Firefox up to v112
.tabbrowser-tab:not([selected]):not([pinned]) .tab-close-button {
visibility: hidden !important;
margin-left: -16px !important;
}
.tabbrowser-tab:not([selected]):not([pinned]):hover .tab-close-button {
visibility: visible !important;
margin-left: 0px !important;
display: -moz-box !important;
}
Instructions
Place this file into the chrome
folder inside your profile’s directory. Follow the directions from Mozilla to find out where to find the profile’s directory location. If the chrome
folder does not exist, you need to create it first.
In the address bar, open about:config and change the following preferences:
browser.tabs.tabClipWidth
to 99 (only needed for older versions of Firefox before v113)
- New versions of Firefox (69+) don’t load the
userChrome.css
on startup by default. Make sure that toolkit.legacyUserProfileCustomizations.stylesheets
is set to true
.
Then just restart Firefox and you are done.
Update 1: It just tried this again myself due to a fresh installation and you also need to change the browser.tabs.tabClipWidth
preference from it’s default value (140) to 99.
Update 2 (August 2017): As pointed out by Veto in the comments below, this functionality is broken since version 55.0.3. The above CSS has been updated to stay compatible with the new Firefox UI.
Update 3 (December 2017): As pointed out in the comments, pinned tabs were affected too. Thanks to Mike for the solution on how this can be avoided. The above CSS has been adjusted.
Update 4 (October 2019): As pointed out in the comments below, Firefox 69 by default doesn’t load the userChrome.css anymore for new installations.
Update 5 (May 2023): I noticed recently that the close button on hover was not working anymore. I first noticed it on Firefox v113 and on another machine with Firefox v112 it is still working. The CSS rules in Firefox slightly changed. Added a new CSS rule for Firefox v113+. Also the clip width change is not necessary anymore.
Original Source: Post on Neowin Forums