Enable Mouse Zoom In Thunderbird

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:
- 0 - Scroll by a number of lines
- 1 - Scroll document by one page
- 2 - Move back and forward in history
- 3 - Make text larger or smaller
- 4 - Scroll text by a number of pixels
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:
- mousewheel.withnokey.action
- mousewheel.withshiftkey.action
- mousewheel.withmetakey.action
- mousewheel.withaltkey.action
- mousewheel.withcontrolkey.action
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.

You said that Outlook isn’t your main email client, so which is your main one?
I think its thunderbird
It is Mozilla Thunderbird.
Awesome! This actually solved my problem… what a stupid bug.
If this is the same bug that I’ve encountered, there may be another fix: (1) hover over open Outlook item in Taskbar, cursor up to hover over Outlook window item, and right-click; (2) this should give you Restore / Move / Size / Minimize / Maximize — choose Move or Size; (3) use your cursor keys, going arbitrarily N/S/E/W, to try to move or size the Outlook window back into view. Basically, the app behaves as though it were open in a 0x0 window, or at a location that’s offscreen, and this will frequently work to resize and/or move the window. Don’t forget to close while resized/moved, so that Outlook remembers the size/position for next time.
THANK YOU Claude!!! I could get the main window to launch but could not get any other message window to show on the desktop. You are my hero!!!!
Solved my issue! 6 years later and this is still problem…
Fantastic. Thank you. Size did the trick.
This solved my Outlook problem, too. Thank you. :)
Thank you so much, this started happening to me today and was causing big problems. You are a life saver, I hope I can help you in some way some day.
You are a god – thank you!
thanks a lot…. work like charm.. :-)
Yah…thanks Claude. I’ve been having the same problem and tried all the suggestions…your solution was the answer. It had resized itself to a 0/0 box. Cheers
Excellent post. This had me baffled even trying to accurately describe the problem. This fixed it for me.
Thank you
Thanks a lot for the article. Don’t know why it happenend, don’t know how it got fixed, but it was really annoying and now it works :-)
Thanks a lot. I was facing this issue from past 3 week. I tried everything but no resolution. The issue was happening intermittently and mainly when I was changing the display of screen ( as i use 2 monitors). The only option i had was to do system restore. But thanks to you.
I’ve been tried to sole this problem for 12hours. Your comment about changing the display of screen helped me a lot!! Thanks!!
Thank you…don’t know why this happened but your instructions helped me fix it. Running Windows 10 and office pro 2007
Great tip! Thanks!
Worked for me, too – thank you!!!
It’s Worked for me, too
thank you very much!
I had a similar issue with Outlook 2013 on Windows 10 and this helped me to fix it. Thank you very much!
Thank you so much. Solved!
Considering you published this in 2012, incredible not been debugged by Microsoft.
Thank you again. M
This problem was faced by only one user logging to TS 2008 r2 using outlook 2010.The issue was resolved.
Thanks.
Great tip. Thank you!!!! If it helps, I had to use the Control Key and the arrow keys at the same time to bring my window back into view. Worked like a charm.
Thank you, this worked !!!!
Man, you are a fucking god. Thanks a lot, what an annoying bug!!
Awesome, this post solved the issue. Many thanks!