[jQuery] "jQuery is not defined" in line 1400 in 1.3.1.1

[jQuery] "jQuery is not defined" in line 1400 in 1.3.1.1


""jQuery is not defined" in line 1400"
Now and then, I'm getting this error in FF.
The line is:
// Clean up added properties in IE to prevent memory leak
if (jQuery.browser.msie)
Is it a known issue or am I mistaken? TIA
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