Okay, I’ve figured out the key combination in FCKeditor that’s causing me grief: I’m used to typing Command + Left Arrow to go to the start of the current line in an editor. While this works as expected in a normal input field, if I do this in FCKEditor it’s interpreted as “back” by the Firefox and takes me back to the previous page, therein losing everything I’ve typed into the editor.
To install keyconfig, just visit this page, click on the link to the latest keyconfig.xpi file, and install the add-on. Once it’s installed and Firefox has restarted, select Tools > Keyconfig in Firefox, select the row named goBackKb that’s set to ⌘Left Arrow and click Disable.
Once I did this, using FCKeditor in Firefox on my Mac became a much more pleasurable experience, what with the whole “you could lost everything with one careless keystroke” somewhat removed.