Can't highlight text in Chrome? Read this. [also affects Firefox now]

That doesn’t mean it’s not a bug in the browser. It only means that Firefox is likely copying code from Chrome. They do that a lot.

The actual spec says, and I’ll quote it this time:

The UA should use the OS-default highlight colors when neither color nor background-color has been specified by the author.

That said, the tech people here could work around this bug. Here’s a direct quote from that other thread: