A fix for Thunderbird’s inability to set a default zoom level

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While the Firefox browser upon which Thunderbird is built has had a native default zoom setting for some time, even the newest Thunderbird 115 build still lacks that feature, despite people having asked for it for years. Why they are so reluctant, I do not know.

At first it seemed that zooming one message to the preferred level using CTRL + mouse scroll would do it, it soon became evident that it would require the zoom action for each new message.

I used to use an addon for Thunderbird to set a default zoom level, but like so many addons, it was abandoned by its developer years ago.

I saw a topic on the Mozilla site about this issue that was posted since the redesign of Thunderbird, showing that it is still a problem for a lot of people. The individual there found an acceptable combination of font size, UI zoom level, and some other related setting (I remember there being three) to make it work, but I found no such thing.

I had an idea the other day. Firefox no longer needs an addon to set the default zoom level, but what if one of the old addons I used to use for that is still workable in Thunderbird?

I used Waterfox for this, but it is functionally the same as Firefox for this. I went into the addons menu, then selected the option for getting new addons, and searched for ‘default zoom.’ There is an addon by that name, the one I used to use. If you right click the “Add to  Firefox” button and select Save Link As… (it should be called “save link TARGET as,” like it was before, but of course Mozilla had to copy the less precise language that Chrome uses, so I have to tell it I am saving the link itself when I am actually saving what the link points to), and the .xpi file downloads.

You can then go into Thunderbird, go into the addons settings, and select the option to install an addon from a local file. Select the .xpi and install it, then tell it yes, I really meant install it when it asks.

Go into the settings for the addon from the addon menu and set the zoom setting to something other than 100% (which does nothing). I used 170%, which is what I also use in the browser. From then on, all the new messages I click on will open at that zoom level by default! I have tested it a few days on all three of my main machines, and it is working well.

Dell XPS 13/9310, i5-1135G7/16GB, KDE Neon 6.2
XPG Xenia 15, i7-9750H/32GB & GTX1660ti, Kubuntu 24.04
Acer Swift Go 14, i5-1335U/16GB, Kubuntu 24.04 (and Win 11)

4 users thanked author for this post.

WCHS, btbs, 69800, NaNoNyMouse

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Sounded good but did not work for me. It is installed and set to 200 but no change.

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Did you look at new, unread messages? On mine it will not zoom the message in if it has been seen before.

Dell XPS 13/9310, i5-1135G7/16GB, KDE Neon 6.2
XPG Xenia 15, i7-9750H/32GB & GTX1660ti, Kubuntu 24.04
Acer Swift Go 14, i5-1335U/16GB, Kubuntu 24.04 (and Win 11)

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Worked fine for me on Linux Mint.

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Try the following, it works, in effect, almost perfectly, at least when run on v115.15.0. Place it into your profile’s “userChrome.css”. Of course, the specific properties’ values will need to be tweaked to achieve what you need (i.e. if you want to zoom in or out & by how much). But these css properties working together should produce the desired effect.

browser#messagepane {
  transform: scale(0.85);
  min-height: 103% !important;
  min-width: 117.5% !important;
  left: -8.8% !important;
  top: -7.5% !important;
  position: relative;
}

1 user thanked author for this post.

wavy

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Later discovered that with the above css the following is also needed.

vbox#attachmentView {
z-index: 1;
top: 100% !important;
position: absolute !important;
min-width: 100% !important;
margin-top: -30px !important;
}

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The css doesn’t work at all. The left side of each message gets completely cut off and the top of the email get margins of several inches.

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