this seems to be a Firefox bug that should be fixed in Firefox 50:
** Bug watch added: Mozilla Bugzilla #1266914
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Touch seeded packages, which is subscribed to ubuntu-themes in Ubuntu.
Firefox search and location boxes have black borders when unselected
Status in ubuntu-mate-artwork package in Ubuntu:
Status in ubuntu-themes package in Ubuntu:
As seen in the attached screen shot the borders around Firefox
location and search entry boxes are black when unselected, but they
should be grey.
The black borders are inconsistent with the rest of the Ubuntu theming
and it looks jarring.
The issue is resolved by styling the 'frame' selector, which Firefox
uses to style the Search and Location entry boxes. Some overrides are
then applied to prevent frames incorrectly rendering borders in other
To observe the issue simply open Firefox and look at the Search or
Location entry boxes while they are unselected, the borders will be
After installing the patched theme doing to same will result in the
borders being rendered using an appropriate shade of grey.
It is possible that some GTK3+ applications may now render frames with
a border where they previously did not. That said, the default
applications in Ubuntu have been checked for this regression and the
appropriate overrides have been added.
The default installed applications in Ubuntu have been tested to
ensure they do not regress in the manner described above.
Should Firefox style the Search and Location entry boxes with a discrete
selector in the future then the styling added to work around the black border
could be removed/updated.
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