In order for us to better investigate this issue you need to add a little more non-personal information.

Please add the troubleshooting information to your post To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

Hi here is dump from troubleshooting

 Application Basics

   Name: Thunderbird
   Version: 45.7.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20170124052806
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts

 Crash Reports
   http://crash-stats.mozilla.com/report/index/bp-89bf1ab4-ae14-499b-8dc3-c0dd12160401 (2/04/2016)
   http://crash-stats.mozilla.com/report/index/bp-aa1da59a-941f-41ac-b939-9788f2160303 (3/03/2016)
   http://crash-stats.mozilla.com/report/index/bp-ac665738-f46c-4aac-8bae-00c922141014 (14/10/2014)
   http://crash-stats.mozilla.com/report/index/bp-f1af5056-0a09-4a03-9609-37cc42131120 (20/11/2013)
   http://crash-stats.mozilla.com/report/index/bp-9cb65517-01ac-4deb-a22f-701ae2131115 (15/11/2013)

 Extensions
   Lightning, 4.7.7, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   McAfee Anti-Spam Thunderbird Extension, 2.0, true, msktbird@mcafee.com
   Export for Thunderbird & Lightning Launcher, 2.0.7, false, {9d4727a2-1562-e247-bbf7-0e26ac63b123}
   Thunderbird Address Book Synchronisation Extension, 1.9.105.1160, false, synchronize@nokia.suite
   ThunderSync, 2.6, false, thundersync@frank.abelbeck

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
     browser.cache.disk.filesystem_reported: 1
     browser.cache.disk.smart_size_cached_value: 358400
     browser.cache.disk.smart_size.first_run: false
     browser.cache.disk.smart_size.use_old_max: false
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 45.7.0
     font.name.monospace.el: Consolas
     font.name.monospace.x-cyrillic: Consolas
     font.name.monospace.x-unicode: Consolas
     font.name.monospace.x-western: Consolas
     font.name.sans-serif.el: Calibri
     font.name.sans-serif.x-cyrillic: Calibri
     font.name.sans-serif.x-unicode: Calibri
     font.name.sans-serif.x-western: Calibri
     font.name.serif.el: Cambria
     font.name.serif.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-western: Cambria
     font.size.fixed.el: 14
     font.size.fixed.x-cyrillic: 14
     font.size.fixed.x-unicode: 14
     font.size.fixed.x-western: 14
     font.size.variable.el: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 17
     font.size.variable.x-western: 17
     gfx.blacklist.direct2d: 3
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 9b05e496-7c74-4b4a-9b97-58b63706dcf
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1486351635
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true

 Graphics

     Adapter Description: Intel(R) HD Graphics Family
     Vendor ID: 0x8086
     Device ID: 0x0116
     Adapter RAM: Unknown
     Adapter Drivers: igdumd64 igd10umd64 igd10umd64 igdumdx32 igd10umd32 igd10umd32
     Driver Version: 8.15.10.2361
     Driver Date: 4-10-2011
     Adapter Description (GPU #2): NVIDIA GeForce GT 525M
     Vendor ID (GPU #2): 0x10de
     Device ID (GPU #2): 0x0df5
     Adapter RAM (GPU #2): 1024
     Adapter Drivers (GPU #2): nvd3dumx,nvwgf2umx,nvwgf2umx nvd3dum,nvwgf2um,nvwgf2um
     Driver Version (GPU #2): 21.21.13.7290
     Driver Date (GPU #2): 9-16-2016
     Direct2D Enabled: Blocked for your graphics driver version.
     DirectWrite Enabled: false (6.2.9200.17568)
     ClearType Parameters: ClearType parameters not found
     WebGL Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics Family Direct3D11 vs_4_1 ps_4_1) -- OpenGL ES 2.0 (ANGLE 2.1.0.316930d51ea9)
     GPU Accelerated Windows: 0

     AzureCanvasBackend: skia
     AzureSkiaAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: cairo

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.12
     4.12

     NSS
     3.21.3 Basic ECC
     3.21.3 Basic ECC

     NSS Util
     3.21.3
     3.21.3

     NSS SSL
     3.21.3 Basic ECC
     3.21.3 Basic ECC

     NSS S/MIME
     3.21.3 Basic ECC
     3.21.3 Basic ECC

http://kb.mozillazine.org/Recovering_deleted_mail_accounts

If I had to guess why it happened I would say McAfee did it again. To selectively loose only the account information from the prefs.js file would indicate that the issue had to happen from internally to Thunderbird. As you are not one of millions, we have to look for a reason.

Givens McAfees long history of Thunderbird breaking activities and the fact their add-on would be trying to interact with each account separately. Not that I have a clue what their add-on does really. I think that will be the cause.