I will take a guess, toggle the hardware acceleration setting On the toolbar > Options > Advanced > general

Did it fix it? What setting do you have now?

Matt, use hardware acceleration was off; I turned it on; no change; tried a power down restart, after; no change.

Other things noticed: If Tbird is reduced to a window from full screen, you cannot left click drag the window at all. No way to move it that I've found so far.

It appears the transparency is logical as well as visual; if you try to click on anything, you are liable to click on the thing that is underneath instead of what seems to be "top layer". So it's very hard to get through the menus, for instance. But closing the right sidebar helped a lot; menu wasn't overlaying that after closing it.

If I select text (in this email, for instance) it selects with an almost black background, with the text still black, so you can't read what you selected (while selected). It wasn't that way before this version, could read it.

well we are down to troubleshooting. Hold shift while starting Thunderbird and continue in safe mode at the prompt. Any change?

Matt, Started up Tbird in safe mode, no change re transparency.

looking at the image, the menu is above the title bar is that normal for you? Has it always been that way?

The menu is at the top, but I don't even see a title bar. Just menu bar and the tabs below it. I THINK there was previously a title bar above the menu bar, but I don't have a Tbird screenshot from a previous version to be sure. When I reduce to a window, there is still no title bar. And I can't grab the window top bar and move it by any means that I've found so far. I don't see any right click options to change that, either.

Matt, I DO have "Windows Aero" turned off, by the way. I find it annoying. I think by default it may be "on" in Win7pro. I just tried turning it "on" in Personalization. There is some slight improvement, in that the lower layers are fuzzy now, and they don't respond to clicks nearby anymore. Also, the reduced window CAN now be sized by grabbing the edges and moving them. The entire window still can't be moved at one time though. I captured the Tbird Error Console window as an image, attached. Couldn't find a way to grab it as a text file.

Matt, Also, there is no "title bar" present on Firefox 46.0 window either. There ARE window control buttons (top right corner) visible, same line as the FF menu bar. In the Tbird v45 window, the window control buttons (top right corner) are not visible, but actually seem to be there, just hidden behind the TBird menu bar. If I hover there for a second, the prompt boxes appear. When the window is reduced, I can also see the "color flare" as you move over those points (visible around the edges of the end of the Tbird menu bar). Just in case of any use.

ok, I doubt this will help, but in a leave no stone approach.

Reinstall from getthunderbird.com

Matt, Reinstall didn't seem to make a difference. I'm considering copying my Profile folder elsewhere, then deleting it from the original location, and then uninstalling Tbird, reinstalling it, to see if it still does the same thing with a freshly created Profile. AFAIK I should be able to put my saved Profile folder back to return everything to the current condition (if the full fresh install makes no difference). LMK if that is a bad or good idea.

Matt, I would save the profiles.ini file also, so the pointer to the Profile would be restored also.

First couple of minutes I have had here in some days.

Instead of changing anything just make a new profile. While Thunderbird makes this a tad ugly. This add-on makes it simple.

https://addons.mozilla.org/en-US/thunderbird/addon/profileswitcher/ After it is installed it adds a menu entry to the file menu to restart with the profile manger. Then a new profile is but a click or two away..

I pointing you to the web version, as you will want to install it in your new profile, even if only to switch back to the old.