I don't know if this will be of any help, but you could try switching over to thoughtbot's capybara-webkit driver. It's an alternative to Selenium that's headless, meaning it doesn't open a browser to run the tests. When I run my tests using this driver (in an RSpec+Capybara setup), all Javascript errors get printed inline with my RSpec output.
I've never tried switching from Selenium to capybara-webkit, so I don't know how feasible this is on an existing project. If you're not doing anything really fancy with Selenium, the transition might be pretty smooth. However, if you depend on being able to watch the tests running in the browser, or have some other specific need for Selenium, then my answer unfortunately won't be of much use.
You can find capybara-webkit here: https://github.com/thoughtbot/capybara-webkit
Getting it installed might be a pain, since you'll need the Qt4 library. If you don't already have Qt4 on your system, the build process can take a long time. For me, it was well worth the trouble. I much prefer capybara-webkit to any other solution I've tried.