Using the diff provided in this thread on MozillaZine's forums, I was able to construct a rudimentary extension that reverts the find bar in Firefox to its original find dialog.
Retro_Find_1.4.1.xpi - 8.34KB - CACA740304D22FEADF3964097F4F7968
maxVersion
to 1.5.0.*
maxVersion
to be compatible with Firefox 1.5Retro_Find_1.4.xpi - 8.34KB - E3687AB10EF862AC417F89324B3CD577
Retro_Find_1.3.xpi - 15.9KB - 216D7A9C093F82079887ACC081E4B5AE
Retro_Find_1.2.xpi - 14.0KB - EEB2C4DDBFE5DE040BC93AF70E44C6D2
Retro_Find_1.1.xpi - 13.2KB - 8BEB3E952F93B8ADA30642E7C84F1D89
Retro_Find_1.0.xpi - 6.09KB - 2AA79115D35B171210251F7E44ACF011