Vimium - The Hacker's Browser.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Tridactyl - Replace Firefox's default control mechanism with one modelled on the one true editor, Vim.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Surfingkeys - Rich shortcuts to click links/switch tabs/scroll pages or capture full page, use Chrome like vim for productivity.
Better Uptime - We call you when your website goes down