The Thunderbird development team released the last version of the 52.x branch a couple of days ago. The next version of Thunderbird will be Thunderbird 60.0 if no last minute minor version is released before it.

Thunderbird 60.0, just like the Firefox 60 release was, is a big release that moves the email client from the old Extended Support Release to the new 60.x development version.

Thunderbird 60 will introduce a lot of new features and changes. Some of these affect the handling of extensions and themes. The changes are not as dramatic as those introduced in Firefox 57 but users may still run into compatibility issues.

Probably the biggest change in regards to extensions is that Thunderbird will only load extensions that are marked as compatible with Thunderbird 60.0 explicitly. Add-ons that are not will be disabled and if you try to install an extension that is not marked as compatible with at least Thunderbird 60.0, you will get the "could not be installed because it is not compatible" error message.

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There is a solution for that though, as you can disable strict compatibility checking to install extensions that are not marked as compatible with Thunderbird 60 explicitly.

Here is how that is done:

1. Select Tools > Options from the menu bar. If the menu bar is not displayed by default tap on the Alt-key on the keyboard to display it.
2. Go to Advanced > General.
3. Click on Config Editor.
4. Search for extensions.strictCompatibility
5. Double-click on the preference.

A value of true means that strict compatibility checking is enabled in Thunderbird, a value of false that it is disabled.

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While that won't make incompatible extensions compatible with the browser, it ensures that compatible extensions that are not listed as compatible by their authors can be installed and enabled.

Once you have flipped the preference to false, you can install extensions to find out if they will install this time.

All extensions listed on the official Thunderbird add-ons website list minimum and maximum compatibility information. Any extension that is listed as compatible with Thunderbird 60.0 or higher will install and run just fine in the email client when version 60.0 gets released.

Extensions that lists a lower version of Thunderbird can still work in Thunderbird 60.0, but those need the flip of the preference unless the author pushes out an update before the official release of Thunderbird 60.0.

You may notice that Options buttons are missing on the Add-ons Manager page. You can display the Add-ons Manager with a click on Tools > Add-ons.

The development team moved the options to Tools > Add-ons Options instead where you find all extensions with options listed. Just select the one that you want to modify and the options open in a new window.

I have no information why the change was made; it feels less intuitive in my opinion as I cannot change the settings of several extensions without having to select Tools > Add-ons Options each time to select another installed extension.

As far as themes are concerned, Thunderbird 60.0 supports WebExtensions themes which you can install just like any other theme in the email client.

Now You: What's your take on these changes?