I'm using Firefox 3.6.15 along with Firebug, and I sporadically get the following JavaScript error on Meta and Stack Overflow when I interact with the profile dropdown:

u.hasClass is not a function
Line 1

(Error taken from Meta)

I can reproduce just by mousing over the dropdown arrow and mousing off from any page.

Reliable steps to reproduce:

  1. Mouse over the down arrow that pops up the profile window
  2. Move your mouse away (off of the dialog resulting from #1) and click the left mouse button
  3. JavaScript error occurs.
  • I can't reproduce this in the exact same environment. Clear your browser cache and try again.
    – Jon Seigel
    Mar 13, 2011 at 16:33
  • @Jon Seigel: Cache is completely disabled on my machine, but I cleared it just in case and I get the same result. Mar 13, 2011 at 16:37
  • I can repro this consistently on Firefox 4 RC1 on Ubuntu, though I don't really want to report this because the net effect of this bug is that clicking the arrow opens the popup, while hover does nothing, and this happens to be the configuration I like :P
    – Yi Jiang
    Mar 13, 2011 at 16:45

1 Answer 1


Good catch; this is what caught us: Why do Firefox setInterval callback arguments differ from other browsers? (except that it was setTimeout, not setInterval in this case).

Learning something new every day :)

Fixed in the next build.

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