> 2nd wild guess: what about disabling ABE outright?
No difference.
Got it! It's the Windows theme that makes the difference.
Windows (7) "Aero" & all is fine.
Change to Windows Classic & the delay becomes apparent.
(Windows 7 Basic is unaffected, but Classic & High Contrast are.)
I run Windows Classic.
(Sorry, but Basic sucks. Aero sucks. They're just not me.)
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.19) Gecko/20110420 SeaMonkey/2.0.14 Pinball NoScript FlashGot AdblockPlus
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.17pre) Gecko/20101216 SeaMonkey/2.0.12pre
I don't know about the OP, but I could definitely reproduce on XP and Fx 3.5.16.
After profiling a bit, I found that the problem is Window's Classic Theme + Firefox (SeaMonkey?) default theme causing textboxes and textareas to take an insane amount of time to be initialized. Since NS 2.0 and above implements internal editing for ABE rules, it exacerbates this (Firefox's? Windows'?) bug, which is present anyway.
Interesting enough, switching to a different browser theme (Lavafox, in my case) cured the symptom.