Another way to describe this would be that the Addressbook seems to be disconnected from the system. I just tried writing to someone from there - same result.

have you actually tried typing in those dialogs..... they are grey until you use them.

You might also use the contact pane. F9 toggles it's state.

Matt, neither of these suggestions makes any difference. Believe me, I tried everything I could dream up before writing, many times! When I use the contact panel, and use "Add to To", the field in the message comes up blank, but white; if I type directly INTO the field, anything I type goes away the minute I move on.

But what's more - I run several accounts through Thunderbird, and NOTHING shows up in the "From" field, nor can I add anything. Even if I could get something into the "To" fields, there's no "From"! It seems that somehow my contacts are disconnected, and also the things I have in the account profiles.

Is this possibly due to POP vs. IMAP? I use T'bird in POP mode, and let the online email deal with itself (occasionally I go into it and clean up).,

I fear I may have to reinstall Thunderbird, and that's something I've never done alone (my #1 "guru" died over a year ago).

Is this "Troubleshooting Information" of any help? Copied to clipboard per instructions and first part pasted below (2nd part to follow):

 Application Basics

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

             (Local drive)
   Application Build ID: 20160205114119
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, false

   account2:
     INCOMING: account2, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account3:
     INCOMING: account3, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account4:
     INCOMING: account4, , (none) Local Folders, plain, passwordCleartext

   account5:
     INCOMING: account5, , (pop3) pop.gmail.com:995, SSL, passwordCleartext
     OUTGOING: , smtp.gmail.com:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (pop3) pop.gmail.com:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account7:
     INCOMING: account7, , (nntp) news:119, plain, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account9:
     INCOMING: account9, , (pop3) pop.googlemail.com:995, SSL, passwordCleartext
     OUTGOING: , smtp.gmail.com:465, SSL, passwordCleartext, true

   account10:
     INCOMING: account10, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

 Crash Reports
   http://crash-stats.mozilla.com/report/index/bp-fb8128fd-675c-4945-a80f-e77ff2130811 (8/11/2013)

 Extensions
   Change quote and reply format, 0.8.6, true, {f6090211-2004-44d8-9090-be3c2adfd66f}
   Image Zoom, 0.6.3.1-signed, true, {1A2D0EC4-75F5-4c91-89C4-3656F6E44B68}
   ImportExportTools, 3.2.4.1, true, {3ed8cc52-86fc-4613-9026-c1ef969da4c3}
   ReminderFox, 2.1.5.4, true, {ada4b710-8346-4b82-8199-5de2b400a6ae}
   Transliterator, 0.9.1.1-signed, true, {07d43380-b306-4a08-a47a-140efd1b4700}
   Zombie Keys, 2.16.1-signed, true, zombiekeys@bolay.de
   Quote Colors, 0.3, false, {B274D460-4DF9-454c-AC69-CA71398D7498}

 Important Modified Preferences

   Name: Value

     accessibility.typeaheadfind.flashBar: 0
     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
     browser.display.foreground_color: #000066
     browser.display.screen_resolution: 96
     browser.zoom.full: true
     dom.apps.reset-permissions: true
     dom.max_chrome_script_run_time: 0
     dom.w3c_touch_events.expose: false
     extensions.lastAppVersion: 45.0
     font.internaluseonly.changed: true
     font.language.group: x-western
     font.minimum-size.x-cyrillic: 12
     font.minimum-size.x-unicode: 13
     font.minimum-size.x-western: 13
     font.name.monospace.el: Bitstream Vera Sans Mono
     font.name.monospace.tr: Bitstream Vera Sans Mono
     font.name.monospace.x-baltic: Consolas
     font.name.monospace.x-central-euro: Bitstream Vera Sans Mono
     font.name.monospace.x-cyrillic: Bitstream Vera Sans Mono
     font.name.monospace.x-unicode: Adjutant
     font.name.monospace.x-user-def: Bitstream Vera Sans Mono
     font.name.monospace.x-western: DejaVu Sans Mono
     font.name.sans-serif.el: WP Greek Helve
     font.name.sans-serif.tr: Calibri
     font.name.sans-serif.x-baltic: Calibri
     font.name.sans-serif.x-central-euro: Calibri
     font.name.sans-serif.x-cyrillic: Calibri
     font.name.sans-serif.x-unicode: Trebuchet MS
     font.name.sans-serif.x-user-def: Arial
     font.name.sans-serif.x-western: Trebuchet MS
     font.name.serif.el: Cambria
     font.name.serif.tr: Cambria
     font.name.serif.x-baltic: Cambria
     font.name.serif.x-central-euro: Cambria
     font.name.serif.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-user-def: Times New Roman
     font.name.serif.x-western: Cambria
     font.size.fixed.x-baltic: 14
     font.size.variable.el: 13
     font.size.variable.tr: 17
     font.size.variable.x-baltic: 17
     font.size.variable.x-central-euro: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 13
     font.size.variable.x-western: 11
     gfx.blacklist.suggested-driver-version: 257.21
     gfx.direct3d.last_used_feature_level_idx: 0
     gfx.driver-init.appVersion: 42.0
     gfx.driver-init.deviceID: 0x68f9
     gfx.driver-init.driverVersion: 12.104.0.0
     gfx.driver-init.feature-d2d: true
     gfx.driver-init.feature-d3d11: true
     gfx.driver-init.status: 2
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 77c9dcf8-989b-40a7-92d3-f830e9c12bc
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"7"},"attachmentCol":{"visible":false…
     mailnews.database.global.views.global.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"5"},"attachmentCol":{"visible":false…
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     network.protocol-handler.app.http: mozilla-firefox
     network.protocol-handler.app.https: mozilla-firefox
     places.database.lastMaintenance: 1454792495
     places.history.expiration.transient_current_max_pages: 79074
     places.history.expiration.transient_optimal_database_size: 85872802
     plugin.disable_full_page_plugin_for_types: audio/mpeg,video/mpeg,audio/x-wav,audio/x-ms-wma,application/pdf
     plugin.importedState: true
     plugins.update.notifyUser: true

Whew! I pasted the whole thing into a text editor and it is LONG!!! You probably don't need all of it. Skipping over the "printer" lines (many of these refer to outdated printers I don't use anymore - is there any way to edit this stuff???), below that is: Graphics

     Adapter Description: ATI Radeon HD 5450
     Vendor ID: 0x1002
     Device ID: 0x68f9
     Adapter RAM: 512
     Adapter Drivers: aticfx32 aticfx32 aticfx32 atiumdag atidxx32 atiumdva
     Driver Version: 12.104.0.0
     Driver Date: 3-28-2013
     Direct2D Enabled: false
     DirectWrite Enabled: false (6.2.9200.17568)
     ClearType Parameters: Gamma: 2200 Pixel Structure: R ClearType Level: 100 Enhanced Contrast: 300
     WebGL Renderer: Google Inc. -- ANGLE (ATI Radeon HD 5450 Direct3D11 vs_5_0 ps_5_0) -- 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
     4.11
     4.11

     NSS
     3.21 Basic ECC
     3.21 Basic ECC

     NSS Util
     3.21
     3.21

     NSS SSL
     3.21 Basic ECC
     3.21 Basic ECC

     NSS S/MIME
     3.21 Basic ECC
     3.21 Basic ECC

Now I find that I can not even compose a message! If I try to write in the message box, nothing shows up.

Can I uninstall/reinstall without losing my years of archived messages, contacts, etc?

I'd try Thunderbird in Safe Mode. You're using several add-ons I don't know, and so can't be sure they aren't related to your troubles.

https://support.mozilla.org/en-US/kb/safe-mode-thunderbird?redirectlocale=en-US&redirectslug=safe-mode

YES, this DID solve the problem, Zenos! Now what is next? Do I try reinstating the add-ons I want one by one??

Er....it solved the problem as long as I was in "Safe Mode", but when I exited and re-started, it came back. Should I do what I suggested: re-start the add-ons I really want one by one, and test?

re-start the add-ons I really want one by one, and test

I would take a punt on it being the change quote and reply as it is the one that directly interacts with the compose process. But it is really a guess.

If you have issues with it, drop Paolo an email. He is usually fairly reasonable when bugs occur, although from his recent post on his web site, a bit disillusioned with Mozilla. But then I am in the same camp.