Note: this probably only applies on Unix-derived operating systems like Linux distributions and Mac OS X.

For work, I make extensive use of Trello. I found that I regularly end up with random URLs of pages I’d visited ending up as attachments on Trello cards I was working on. Because this happened seemingly at random, it was a bit of a privacy issue.

Today, I discovered the mechanism that caused this. Apparently, selecting text in Firefox is enough to copy that to a Firefox-internal clipboard. Clicking the middle mouse button or scrollwheel pastes from that clipboard.

I’m sure this can be useful to some, but for the above reasons I was eager to turn it off.

Here’s how you do it:

1. Open a new tab and enter about:config in the URL field. Accept the risks with the button you’re shown.
2. Search for the setting clipboard.autocopy, and switch it to false with the button on the right. This will turn off the automatic copy upon making a text selection
3. Search for the setting middlemouse.paste, and switch it to false as well. This, as the name suggests, turns off the paste action upon clicking the middle mouse button.

I hope this helped you. Happy browsing.