Ok, I have a version that works in Chrome, available at
https://gist.github.com/3724409.
This version actually should be compatible with all modern (IE9+) browsers, though I haven't done any testing. It uses capability detection to ensure that IE8 users won't even see the show/hide link. So once a few people test it, we can add it to L19 if the admins so desire. I will probably try to make it work in IE8 this evening or in the next few days (sorry, IE7 won't happen unless you bribe me).
For people who know what a tar.gz file is, the simple way to install in Chrome (sorry, I don't know about Firefox, Safari, IE or Opera):
1. Copy paste the two code snippets into manifest.json files and showhide.js files in their own folder on your computer.
2. Go to extensions in Chrome, located under the wrench menu that's to the right of the location bar.
3. If it's not already checked, check the box for "developer mode". You should know see button reading "load unpacked extension" and "pack extension".
4. Click "load unpacked extension". This will give you a file browser, select the folder that contains the two files.