Domain-name search Firefox feature
Installing this into Firefox (takes < 1 minute and doesn't require a download) allows you to check for the availability of domain names straight from the browser.
It was created by my colleague, who works with me at easyname.eu, but it was his idea, and I genuinely think it's a cool feature!
P.S. I recently created a nerdy privacy-respecting tool called When Will I Run Out Of Money? It's available for free if you want to check it out.