It's been a good week for new (to me) Firefox extensions.
Any serious Firefox user will tell you that it's all about the extensions. Unfortunately, if you install enough extensions, you'll eventually encounter a conflict between the hotkeys registered by different extensions. A few extensions are nice enough to allow you to redefine the hotkeys. Most do not. I've been struggling with this lately - the Focus Last Selected Tab and Image Zoom extensions register conflicting hotkeys - I've been wanting to use the FLST version, but Image Zoom was taking priority.
I just ran across the keyconfig extension, which solved my problem handily. It allowed me to suppress the Image Zoom hotkey (it can also reassign operations to a different hotkey). Problem solved.