I've spotted what seems to be an unusual bug in sql.js.
Steps to reproduce:
* Open firefox
* Open firebug console
* Go to main.php
* Click on the SQL tab
* Enter this query: USE somedb
* Click "Go"
At this point your firebug console should be busy displaying a dozen of requests for JS files which are totally unnecessary and the database that you attempted to select has not been selected for you.
Now, onto the interesting part, git-bisect says that the bug comes from commit 44364aae1bf51847744b53dfc773ad0415efba6b.
The commit itself looks quite harmless, but somehow it manages to break this functionality.
In fact, if in current master you replace 'isAddClass' on lines 549 and 562 back to 'class', the issue disappears.
As far as I can see, this issue is only present in Firefox (I'm using version 12.0).
I tested Chromium 18.0 and IE 8, however they do not have this issue.