Firefox goes to great lengths to preserve the user's work. For the rare cases when it fails, read this.
If I browse for some time, opening a bazillion tabs before the computer crashes, firefox will offer to restore those tabs as soon as I start it again.
If I type some text in a <TEXTAREA/> form before the computer crashes, firefox will restore the text.
Then, I loaded the resulting html file into a separate firefox tab: the hexadecimal sequences were interpreted, and the HTML code was rendered. Copy-pasting the HTML into WikEd lost the HTML formatting but keep the ASCII text, which is exactly what I wanted. My changes were recovered! Thank you, firefox.