Firefox tweaking done properly http://www.tweakguides.com/Firefox_1.html - Lifehack top list must have taken 5 min. to spit out. Could have consisted of whatever. Direct link to user.js file which you can modify but remember not to touch about:config unless you know what you are doing! No. 12 has the year old wrong value of 30 - 8 is still max. Take seconds to research but faster to copy and paste. Ram vs. hd! Down with poor top lists made hoping to attract attention - such lists can be useful.

Unfortunately I think you are right - may be reason why they keep setting hidden ;) Im wondering if it is a conflict with other extension or just build in bug. Search their forum http://imagezoom.yellowgorilla.net/forums/ for "image resize", may be "autofit" - where I found the setting. Did not find any complaints. Worth a test cause it does seem to work.