Was using TB normally, without any observed odd computer behavior. Finished sending a message OK. Navigating the message list, which appeared normal, and opened the next message to read. First noticed problems when this message opened. Some of the header element text was missing (not hidden, different color, etc., actually missing), like the "From:" field, and "Subject:" field but not the "To:" field. The message's body was also gone. Menus, their text, and UI icons all appeared normal. Displaying message source for the affected message opened a new winds which was titled properly, and had it's menubar OK, but no source text content. Closed that message and tried to open others, some from listings from another configured e-mail account on my same profile, all with the same symptoms. Called up the About Thunderbird dialog from the menu, which appeared with the logo graphics and the word "updates", but no other text (e.g. the version information that should be displayed there). Restarted with add-ons disabled, and was confronted with the Safe Mode options dialog which had dialog box buttons with their text, but no text in the dialog box itself to explain what it was for (I know the text by memory, and navigated it fine). I noticed that the message listings and the folder trees appear normal, along with the menubars and text and icons, but opening any message still resulted in the same missing text symptoms. At this point I also became aware that command tooltip text was missing also, with a tiny box appearing to hold the tooltip text, but no text (which also happens either in normal startup or safe-mode). Suspecting perhaps a problem with the user profile, I restarted with the command line argument to call up the Profile Manager, and found that it too was missing most of the text from its dialog boxes (see attached picture--which demonstrates the symptoms which now confront me generally). I sucessfully navigated the Profile Manager dialog in the blind to create a new secondary profile to test with, which confront's me with all the normal new-profile initial setup tasks, but all of this stuff is missing UI text! So it's not apparently related to add-ons, and it's not apparently related to bad data in a profile (2nd picture shows result of fresh start in new profile). What gives? Any ideas? Not sure how to approach further troubleshooting. I will restate that these symptoms began while in the middle of an otherwise normal session with Thunderbird, no prior crash or any error. All other running applications remain normal. Newly started applications (such as this instance of Firefox in which I now compose this post) also appear normal. I work in plain-text mode also, and the only help I could google-up was related to much older Thunderbird versions and rendering of HTML messages. Not applicable here, this seems to be manifest on a deeper application level. It's late for me now, and I am shutting down. I'll boot back up fresh and clean later in the day and insure it wasn't a fluky Windows thing, but as all the other apps and app starts are normal, it doesn't seem like that'll be an issue. Preemptive thanks be upon you, dear readers!