The menu and tab navigation go transparent/white such that I can't read them when Firefox loses focus
I've tried all of the three themes that Firefox Quantum comes with, and all of them exhibit this same behavior, where once the whole Firefox window loses focus, that full area up there goes this odd bright transparent that just makes it harder to read everything. Since I use multiple monitors there are times I may not have Firefox on focus but still on screen and want to click on the menu or the tab navigation buttons (scroll left or right or new tab (+) or the list of open tabs).
I've attached two images, the one with red text is off focus, the other is with focus.
Update your Video Card Drivers.
Or move to the ESR Version Going back : unfortunately 56.0.2 and below is no longer safe to use for every day use do to secuity issues, but 52.5.0 ESR is. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018.
You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
Please let us know if this solved your issue or if need further assistance.