Brendan Eich gave the sum to the Proposition 8 fund, which topped $39m and, at the time, successfully revoked gay couples' equal marriage rights by state-wide ballot.
Californian law required donors to list their employers on lists that were published by the LA Times.
Mr Eich was the only person listed as an employee of the Mozilla Corporation, which runs the web browser Firefox, to donate against marriage equality, with three other employees giving a total of $1,350 in favour of equal marriage rights.
As Mr Eich pointed out last night, Mozilla had no control over employees' donations.
via Pink News