Thunderbird joins Firefox on the monthly treadmill

We'll see if messaging client can keep up with sibling browser

Mozilla has lobbed out Firefox 138, and subsidiary MZLA's Thunderbird 138 isn't far behind. The venerable messaging client is picking up the pace and finally syncing its stride with the browser that spawned it.

The new version of Firefox boasts some fresh features, but there's a catch. Mozilla decided on a phased rollout, or as its release notes put it, one new feature "is now available to almost all users worldwide." Apparently, that does not cover the Irish Sea wing of Vulture Towers.

Firefox 138 now lets you copy the URL even of a background tab. Other new niftiness will, allegedly, follow – click to enlarge

So, if you are somewhere far from here, you may get to enjoy improved profile handling with custom avatars and friendly, human-readable names. That's welcome – The Reg FOSS desk's current profile is called 70tmx4ga.default, which doesn't exactly trip off the tongue. Most people probably only need a single profile, but Firefox has a habit of occasionally spawning new ones and it can get cluttered. For those who aren't command-line jockeys, one can manage profiles by going to the special URL about:profiles, or go to the "Help" menu and look under "More troubleshooting information" for the last line in the first section, "Application Basics."

Mozilla continues to double down on its improved vertical tab bar. You can group tabs by dragging one onto another and rearrange groups with drag-and-drop. It sounds good but we haven't been able to try it. Mac and Linux users can now copy the URL of background tabs – that worked for us, and while it's not essential we can see it being handy.

The built-in vertical tab bar is working well and once again we commend it to you. We have vertical tabs, a vertical dock or panel or taskbar according to desktop, and vertical toolbars in apps. Any software which can't do that gets junked, sharpish. Those who are not used to vertical toolbars – or Google Chrome – may be briefly disoriented, but stick with it, it's worth it. It makes much more efficient use of widescreens. There are a lot of laptops around this vulture's dwelling, and we've been gradually removing other vertical-tab extensions from them all: Tree Style Tabs, Vertical Tabs Reloaded, Sidebery, Vertigo Tabs, Tab Center Reborn – we've tried them all, but the built-in ones are good enough and we're purging all the alternatives.

This is the latest monthly refresh for Firefox, following the rapid monthly release cycle that Mozilla has stuck to for the last decade. That's a bit too quick for large organizations, so there is also a much slower-moving Extended Support Release version too, with a roughly annual release cycle. The current Firefox ESR version is Firefox 128, although as we reported when that came out in July 2024, updates are still regularly arriving for the previous ESR release, Firefox 115. The Reg FOSS desk has machines with both Windows 7 and macOS 10.13, both of which can't run any newer Firefox, and they're both still getting updates.

This focus on release schedules matters because for the last few years, the separately owned and run Thunderbird messaging client has only seen major releases based on Firefox ESR versions, as we explained when Thunderbird 102 appeared. But that's now changed.

In a change announced back in February, Thunderbird releases now track Firefox ones, in what MZLA calls the Desktop Release Channel. The previous cycle is still available, but this version has been renamed to Extended Support Release to match Firefox.

This means that Thunderbird 138 is the third release in the new cadence, following Thunderbird 137 on April Fool's Day – so you could say that they got us – and Thunderbird 136.

There weren't many functional changes in these releases. There's a new dark mode, which can override formatting in emails, and a message notifier tray applet, although 137 temporarily disabled this on Linux. However, all three versions have fixed quite a lot of bugs. We switched last month, and the latest versions look substantially the same as before and work fine.

We have heard many reports of people who dislike the new "Nebula" UI, but most things can be customized. For example, you can replace the card-style message pane with a traditional list, which Thunderbird calls Table view – it's the very last button in the main toolbar, way over on the right. We'd like to see MZLA put more effort into grouping all the UI options into fewer places, to make them easier to find, but they are there if you search.

If you really can't get on with Thunderbird's new look, though, you may find Betterbird more to your taste. It's a friendly fork of Thunderbird by a former Mozilla developer named Jörg Knobloch, regularly resynching with upstream with a lot of look-and-feel tweaks, as the release notes detail. The latest version is 128.10, so it follows close on the heels of the upstream project. ®