Although It's less about guns and more about paying/donating to projects on GPL. If you don't know where to donate, start with Firefox. Every £ matters
Mozilla do spend a lot of money on software development, 220 million last year, out of total expenses of 425 million which came from a taking of 593 million of which 81% comes from Google.
For preserving GPL let me suggest donating to Software Freedom Conservancy which is directly related to fighting abuses of open source / free software / libre software licences.