Was the button provided by an add-on? If so, you can bypass its effects by running in safe mode: close TB and then hold Shift when you launch the program. If it was an add-on, remove it from Tools/Add-ons/Extensions and restart TB in normal mode.

Thank you for replying so promptly. I tried as you requested but it didn't work. The zoom button was on the menu and now it is so big that it is off the screen so I can't access it to make it smaller. I've been working on a solution for weeks and can't find an answer. I hate to have to take it to a repair shop, I can't afford it. I have tried several times to delete it and reinstall it but it just comes back.

Did you actually run in safe mode? You should see a window as in the attached picture. There is no zoom button in the default layout of TB, which is what would have been applied if you ran in safe mode. Did you change the preference layout.css.devPixelsPerPx in Config. editor, which is one way to zoom the entire TB interface? If you did, there is a way to restore the display without starting TB. Or, did you use the W10 Magnifier?

Hello Mary, Could you tell us what sort of computer you’re using? Is it a PC with Windows maybe, or a Mac ? Does the magnification affect just Thunderbird or other apps as well?

Hi John, My computer is a desktop Lenovo running windows 10, I really don't know if the zoom works on other things as well, I seldom use it, I can't even remember now why I needed it in the first place, if you could give me something else to try I'd be most grateful.

does you mouse have a scroll wheel? If yes hold the Ctrl key and scroll the wheel. It will make it bigger one way and smaller the other.

Otherwise use the Ctrl key and the minus key (-) to make it a little smaller each time you press it. Conversely Ctrl and the plus key (+) make it bigger

Thank you for answering John. I tried what you suggested and it doesn't work, do you know if it's possible to completely delete thunderbird to start off with a fresh download, I tried several times deleting and reinstalling but it comes back with everything the same, thanks, mary

Please try this:

• click on the Menu app icon (3 lines)
• select 'Options' which will open in a new tab
• In left column click on 'Advanced' - it is the last item in list.
• Click on 'Config Editor' button located bottom right - make window wider if necessary to see it. You may also need to scroll down.
• You may get a friendly warning, but click on 'I accept the risk'.

The 'about: config' window opens within the tab.

• In search type: pixels
• Look for this line: layout.css.devPixelsPerPx
• The default Value should be -1.0

If you do not have Value set as -1.0:

• Right click on that line and select 'Reset'
• Close the 'about:config' window using top right X.

Did this reset everything?

Another idea: Hold down the 'Ctrl' key and press the zero number key (0) to force reset.

I'm sorry, I tried to do as you suggested with thunderbird site open but the screen is so large there is no menu (3lines), on the screen, I tried your other suggestion but it didn't work either, really appreciate your help, thank you, mary

Hi Mary It would help if you could upload a screenshot so we could see what your screen looks like. There are other settings that might have this effect - but the Thunderbird Zoom on its own should not make Thunderbird bigger than the screen. If Thunderbird Zoom is zoomed, then 'hold ctrl button and press zero' should have reset it to normal. Each screen has buttons - usually on the right side or the bottom edge - to manage the size of the display. Can you find those and choose reset everything, or reduce the height and width settings? Can you see the Windows toolbar at the bottom of the screen? If so, right click on the blank part of that bar. Choose Show windows side by side. That should allow you to see the top of the Thunderbird window and get to the menu options. If not, try Show windows stacked, or Cascade windows. If those options still go off the top of the screen, or you cannot see the Windows bar at the bottom ... Here are some keyboard tips to move windows around on your screen https://www.technipages.com/bring-off-screen-window-back-onto-screen Again, using those ideas you may be able to get Thunderbird's top bar back where you can see it. Once you can see the top bar - in the top right corner, you should see a minus sign, a square, then X. If the square is 2 squares overlapping each other, click on it to switch out of full screen mode. The Thunderbird window should get smaller and allow you to move it around to where you want it. I hope one of these tips may help. Good luck! Agnes

Agnes, thank you so much for the information you sent. I am unable to follow the instructions because I can't access the menu bar, the top screen has the menu bar as far as the help the rest of the bar is missing, I tried the side by side, that didn't work either so I've decided to just give up, I've been trying for over a month to solve this and now I'm getting headaches so I will just use another email client, again thank you and thanks to all the other kind people who tried to help me, mary