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.

Please also add the result of these troubleshooting steps to your post

• Does Thunderbird work in TB Safe mode (see Thunderbird Safe Mode)?
• Do you use anti-virus and firewall software? What is the version?

Yes, the forward button is active in safe mode; I use AVG for my antivirus and firewall - this has never caused an issue in the past. The version is 17.5.3022 Here is the troubleshooting info:

Application Basics Name Thunderbird Version 52.2.1 User Agent Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 Profile Folder (Local drive) Application Build ID 20170622064432 Enabled Plugins about:plugins Build Configuration about:buildconfig Memory Use about:memory Profiles about:profiles Mail and News Accounts ID Incoming server Outgoing servers Name Connection security Authentication method Name Connection security Authentication method Default? account1 (pop3) pop.gmail.com:995 SSL passwordCleartext smtp.gmail.com:465 SSL OAuth2 true account2 (none) Local Folders plain passwordCleartext Crash Reports Report ID Submitted Extensions Name Version Enabled ID Lightning 5.4.2.1 false {e2fda1a4-762b-4020-b5ad-a41df1933103} 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 52.2.1 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 mail.openMessageBehavior.version 1 mail.winsearch.firstRunDone true mailnews.database.global.datastore.id 65d48007-e77a-467b-8956-45051399329 mailnews.database.global.views.conversation.columns {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"3"},"attachmentCol":{"visible":false… media.gmp.storage.version.observed 1 network.cookie.prefsMigrated true network.predictor.cleaned-up true places.database.lastMaintenance 1501261999 places.history.expiration.transient_current_max_pages 122334 plugin.importedState true privacy.donottrackheader.enabled true security.sandbox.content.tempDirSuffix {6836cb85-7f7b-4bbe-9534-97ecddb802b3} Graphics GPU #1 Description Intel(R) HD Graphics 3000 Vendor ID 0x8086 Device ID 0x0126 RAM Unknown Drivers igdumd64 igd10umd64 igd10umd64 igdumd32 igd10umd32 igd10umd32 Driver Version 9.17.10.4459 Driver Date 5-19-2016 Features Direct2D false DirectWrite true (10.0.15063.413) WebGL Renderer false AzureCanvasBackend skia AzureCanvasAccelerated 0 AzureFallbackCanvasBackend cairo AzureContentBackend skia JavaScript Incremental GC 1 Accessibility Activated 0 Prevent Accessibility 0 Library Versions

Expected minimum version Version in use NSPR 4.13.1 4.13.1 NSS 3.28.5 3.28.5 NSS Util 3.28.5 3.28.5 NSS SSL 3.28.5 3.28.5 NSS S/MIME 3.28.5 3.28.5

Hold Shift when you launch TB, and when the safe mode window appears, check 'Reset toolbars and controls' and click 'Make changes and restart'. Does that make the forward button active?

Yes, this seems to have fixed the problem. Thanks to your team for all your help!