Mozilla Firefox/Thunderbird “legacy” addons (#E6F3)

News from the friendly crackpots over at Mozilla:



You are receiving this email because you are listed as a developer of a legacy add-on on (AMO). Mozilla will stop supporting Firefox Extended Support Release (ESR) 52, the final release that is compatible with legacy add-ons, on September 5, 2018.
As no supported versions of Firefox will be compatible with legacy add-ons after this date, we will start the process of disabling legacy add-on versions on AMO. On September 6, 2018, submissions for new legacy add-on versions will be disabled. All legacy add-on versions will be disabled by early October 2018. Once this happens, users will no longer be able to find your legacy versions on AMO.
After legacy add-ons are disabled, you will still be able to port your extension to the WebExtensions APIs. Once your new version is submitted to AMO, users who have previously installed your extension will automatically receive the update and your listing will appear in the gallery.
You can find more information about porting legacy extensions to the WebExtensions API on MDN, and we encourage you to visit our wiki for more information about upcoming development work and how to get in touch with our team if you need any help.
The Add-ons Team
You have received this email because you are a registered add-on developer on and you have at least one legacy extension associated with your account. If you do not want to receive these updates about your AMO account and legacy extensions, please sign in to and remove your legacy extensions.
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Mozilla Privacy Notice

Well, thank you very much. Firefox is down to 10% global market share (from…40?) because of massive design fails, and now you idiots will halve that again with the stupid forced Webex addon thing and kicking out all “legacy” XUL addons. Good luck, I can stay basically forever on FF 52.9 and TB60. Or I can change to Chrome, like half of the world has already done. Great idea to prefer hated UI redesign over speed improvements, fixes of memory holes or just plain integration of must-have features that had to be delivered for ages by popular addons.

Here’s the summary for Thunderbird:
* If you’re using up to TB57 (most people should be at TB52 ESR), use version 64.3 from the archive. Even though Mozilla may state that there are no compatible versions: There ARE. 64.4+ will NOT work.

* If you’re using TB58+ (TB60 is current as of now, which was released on August 6th), use version 64.4 or newer, basically whatever your TB will offer you for installation. 64.3- will NOT work.

How did I know there’s a new Thunderbird release? Easy! Just watch the blog access numbers go through the roof:

(This post wraps up the former #E6/#E6F1 and #E6F2 posts that still contain the files for manual downloading…let’s say for the unlikely event that Mozilla will take them down as well.)

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Dan C.

Thank you for clearing this up in Plain English! I’m currently running TB 52.9.1 (32-bit). So when I get to TB58+ that’s when I have to start to use your version 64.4+ TFSC. :good:


Dan C.
Staten Island, NY


Hi. I’m on the Thunderbird Beta, and was updated last night to 63.0b1. Most of my add-ons were automatically disabled and marked as incompatible. TFSC – I was running 64.4 – wasn’t, but there’s a problem. All the text in TB shrunk, as if TFSC wasn’t working or had all been set back to default values, and the toolbar button has disappeared, as has the entry in the tools menu, leaving no way to call it up and view/change any settings in it. The add-on options are still accessible, but that just gives the options to hide the tools and app menus and abbreviate the toolbar button text. I discovered that there was a TFSC version 64.5 and installed that, but it has made no difference – I still have no toolbar button or entry in the tools menu. Is there a TB config file setting I can check and/or a TFSC config file I can maybe load and edit in a text editor? At the moment I’m trying to figure out what settings to put in a userChrome.css file to get back to the display i want, but I’d much rather have a working TFSC if possible – for which, much thanks.


I went from TB 60 beta 11 (which should have been very nearly the same if not actually the same as 60.2.1 as it was the last beta before the 60.2.1 general release) to 63.0 beta1. TFSC 64.4 did work fine with TB 60b11 for me, and that’s on a Windows 10 machine. I did see what you quoted above in the changelogs, so was a bit surprised that TFSC plus one other add-on weren’t disabled after the update to 63b1, when 6 other add-ons were. But then found it wasn’t working as I described above. If there’s any trouble shooting I can do, finding and reading of logs or whatever, please let me know.


OK, thanks for looking and explaining. I switched to the beta tracks a few months ago because it contained a fix for something that had been annoying me, and some other features that were nice. All of that is now in the new stable version, and I can’t see anything else in the new beta I’m bothered about, so I will go back to the stable track for now. Thanks again for creating this add-on.

Mike Hardy

I’m looking for something completely different (how to target thunderbird correctly in the new manifest.json) but saw this. I’ve already solved this problem and you might like the backwards-compatible snippet

// Use ChromeUtils instead of XPCOMUtils here and line 154 for TB64+ (or earlier?)
&& XPCOMUtils.generateQI([Ci.nsICommandLineHandler, Ci.nsIClassInfo, Ci.nsIFactory]))
|| ChromeUtils.generateQI([Ci.nsICommandLineHandler, Ci.nsIClassInfo, Ci.nsIFactory]),

Bill Cohen

This add-on is a God-send for people like myself with poor vision.

Will you be tackling the full webextension needed for the
latest Thunderbird versions (68 and 70 and afterwards)?

I’d be glad to send a small contribution if that helps!


Steve W

Thanks for the update. I also rely on TFSC. The scale factors I use most are 120% and 140%, depending on what monitor I’m using.


Another option – the one I use – is to create a userChrome.css file and put it in the profile ‘chrome’ folder (create it if the folder doesn’t already exist).

In a text editor, put the following:

* Do not remove the @namespace line — it’s required for correct functioning
@namespace url(“”); /* set default namespace to XUL */

* {
font-size: 11pt !important;
font-family: “Verdana” !important;

Save as a .css file and put it in the chrome folder in the profile. Obviously you can change the font size and font family to taste. (I also change the folder tree, thread tree and message pane colours in mine.)


Finally someone to explain us programming illiterates how to change this on the interface level. Thank you, David, that’s very useful!


Do you have a compatible version of Thunderbird email app – Theme font changer for MAC MOJAVE?

Steven Wertheimer

I don’t use this add-on anymore. I just change the layout.css.devPixelsPerPx setting using the config editor. Works great and no need to install an add-on.


Silly me allowed Avast to update out of date – and lost my beautiful Thunderbird 60.2 with your wonderful to those of us with bad eyesight – ability to change fonts on Thunderbird. Now I find that although I disabled the update to Never. Still as soon as I got it re-set up – it was updating. So again went through and having turned off internet connection thought safe – but NO – it was updating again. Somehow after around 6 or more attempts – I got it and managed to stop updating in its tracks but not for long I suspect – as soon as I close down and restart tomorrow will find back to 68 or whatever latest is and I cant read the blooming small fonts…………….Beats me how it can update with all seemingly disconnected even
Why oh why are the team at Mozilla so small minded? :suspect: Bet they are all climate change warriors out gluing themselves to the roads in spare time. Lot of that with so many deserting Firefox due to same thing – not allowing anyone to use programs they dislike. I cant read small print here – used wordpad so could see what I had written. Having to have Cararats done didnt help either.


use 60.9.1 and block updating…it works for me

Joseph Donahue

I don’t know why people like Chrome so much. It’s actually very slow to load and very power hungry. Microsoft Edge is a much better alternative. Seriously.

Joseph Donahue

I seriously love your site.. Very nice colors & theme. Did you create this website yourself? Please reply back as I’m looking to create my own personal site and would like to know where you got this from or what the theme is called.