https://addons.mozilla.org/en-US/firefox/addon/firessh/
Handy little add-on for Firefox. Can’t really speak well to its stability and functionality, as I almost always have PuTTY available on my system and configured for very convenient access, but it seems to be well-received, and it fits in well if you follow the “everything in a browser” mentality. Definitely noteworthy that it supports tunneling.