We'll try to make this a preference in a near future release, but for now you can manually change the hot key by unzipping zotero.jar (we'll have a "Modifying Zotero Code" page up shortly in the developers wiki to explain this process in more detail) and then altering the overlay.xul file. At the end of the file you'll see:
Just change the key (and/or the modifiers) to whatever you want and then follow the instructions in "Modifying Zotero Code" to convert the unzipped Zotero files back into zotero.jar and restart Firefox.
You can also change the keystroke with the keyconfig extension (http://extensionroom.mozdev.org/more-info/keyconfig) -- it won't yet install by default with Firefox 2.0, but you can enable it with the Nightly Tester Tools.
We recently realized that Cmd-Shift-Z/Ctrl-Shift-Z is the Redo keystroke on Mac/Unix (it still seems to work fine in Firefox 2.0, which is why we didn't notice it, but it doesn't appear to work in Minefield), so we'll be changing the default shortcut to Cmd-Option-z on Mac and Ctrl-Alt-z on Windows/Unix. But you can use keyconfig to change the Redo keystroke if necessary and keep the existing shortcut.
Upgrade Storage
<keyset id="mainKeyset">
<key id="key_openZotero"
key="Z"
oncommand="ZoteroPane.toggleDisplay();"
modifiers="shift accel" />
</keyset>
Just change the key (and/or the modifiers) to whatever you want and then follow the instructions in "Modifying Zotero Code" to convert the unzipped Zotero files back into zotero.jar and restart Firefox.
We recently realized that Cmd-Shift-Z/Ctrl-Shift-Z is the Redo keystroke on Mac/Unix (it still seems to work fine in Firefox 2.0, which is why we didn't notice it, but it doesn't appear to work in Minefield), so we'll be changing the default shortcut to Cmd-Option-z on Mac and Ctrl-Alt-z on Windows/Unix. But you can use keyconfig to change the Redo keystroke if necessary and keep the existing shortcut.