Users of the Thunderbird email client can zoom the text of email messages by holding down Ctrl and tapping on + to increase the font size or - to reduce it.
The zooming options are furthermore available under the View > Zoom menu in the menubar of the email client.
There is however no option to zoom in our out with the mouse which some users may find more comfortable than using the keyboard shortcut or accessing the zoom options on the menubar.
Thunderbird supports mouse zooming but it needs to be activated in the advanced configuration menu before it becomes available.
Users need to click on Tools > Options to open the general Thunderbird options. They then need to switch to the Advanced > General tab in the window to access the Config Editor of the email client.
This opens the about:config window. The easiest way to find the correct parameter is to enter it into the filter form at the top. Enter mousewheel.withcontrolkey.action in the filter form and hit enter.
This parameter defines the mousewheel action when it is used and the Control key is active.
Only one parameter should be displayed in the listing now.
The default setting is set to scroll the document by a number of lines.
Update: the new default setting in recent versions of Thunderbird is 3 which makes text larger or smaller.
Possible values are:
A double-click on the parameter opens an edit form so that the value can be edited. Changing the value from 0 to 3 changes the behavior so that a combination of Ctrl and the mousewheel now zooms in or out.
Please note that there are additional parameters available that can be configured this way as well:
To display all of them at once filter for the parameter mousewheel.with.
The preference mousewheel.withnokey.action for instance defines the mousewheel action when it is used. It is in theory possible to switch it to zoom from scrolling if you prefer that.
The only key that has a different functionality by default is the alt key which in combination with the mousewheel scrolls the document by one page.
Thunderbird users who prefer to use the Shift key instead of Control need to change the value of the mousewheel.withshiftkey.action parameter to 3 instead.
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