Affected versions

• 71.0a1
• 72.0a2
• 71.0b4

Affected platforms

• Windows 7
• Windows 10

Steps to reproduce

• Preconditions:
  The OS must have a high contrast theme activated.
  Google must be the default search engine.

1. Launch Firefox.
2. Type a search term in the Awesome Bar.
3. Navigate through the search result.

Expected result

• The search result page is displayed properly and can be navigated.

Actual result

• The search result page has a black square over the resulted websites.

Regression range

• Will look for a regression ASAP.

Additional notes

• Also the bing.com is also affected (https://tinyurl.com/y4ry3tyk).
• Please note the attachments: high_contrast_bug.gif

[Tracking Requested - why for this release]: Web content does not show properly In HDM

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=86961574004badd8018688be05557509afb08982&tochange=6baef669e147828062e93a6e7edec259853e7304

Regressed by :
Fri Oct 04 18:24:40 2019 +0000 6baef669e147828062e93a6e7edec259853e7304 Morgan Reschenberg — Bug 1539212: Add readability backplate for all elements containing text when HCM or a11y theme is active. r=dholbert,mattwoodrow,Jamie

Another steps to reproduce(maybe only in Japanese region):
Google settings -> Search Settingss -> Region Settings Japan
Google settings -> Languages ->日本語
Just open https://www.google.com/search?client=firefox-b-d&q=ppp
( reproducible with any method, e.g open from bookmarks/address bar)

Hello! Thanks for filing. This is being addressed in this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1587127
Marking as a duplicate :)