Affected versions

• 68.0, 69.0b6, 70.0a1 (2019-07-16)

Affected platforms

• Windows 8.1;

Steps to reproduce

1. Set up the Windows theme to be grey;
2. Launch Firefox, change it to Dark theme;
3. Select any other tab;

** Set Windows color scheme:**

• right click on desktop;
• click on Personalise;
• click on Color;
• pick the Grey one;
• Click on Save changes.

Expected result

• Add new tab button is visible;

Actual result

• Color setup for the Add new tab button makes the + symbol barely visible;

Regression range

• First bad: build_date: 2017-07-28 changeset: 5845151f1a2cd00957fdd48e204542ccbdfaba1e
• Last good: build_date: 2017-07-27 changeset: 36f95aeb4c77f7cf3b3366583008cd6e4b6b1dba
• Pushlog: URL;
• Potential regressor: bug 1370929

Additional notes

• attached recording with the issue;