Something about this 13.5 update has changed things. A few image links I use every day is in Full Zoom mode before I even click it and so far a couple other sites were zoomed in w/o me doing anything so i have to reset the settings. I hope I don't have to do this for every site now. I was going to go back to the older version where it worked but now Firefox doesn't give us the download button for older versions which is real bad. Sometimes being able to go back to the 'working' version is the only fix until the new version issues are resolved.

p.s. I never messed with the pref's before.. I only adjusted the button settings. I understand most of what the Pref's are for but not all. I'll give it a shot.

p.p.s. Not having messed with the pref's before, this so far seemed to work -> I UNchecked the 'Enable fit-to-window' option in the Image Scaling section being you mentioned that in your update notes which was checked by default. At first nothing changed until I finally scrolled to the 'bottom' of the Pref's page & found the Save button [my fault]. I'm assuming that option is checked by default because I never messed with Prefs - Maybe this might help others.. I don't know. If you change anything, I'll remember I changed that option in case it needs to be rechecked again.