One of the many sudden problems I've had with FF in the last itterations is the zoom keeps going back to say, Ctl 0 set. I've found a fix for what used not to be a problem, but it's very handy as it fixes a zoom for all regular sites.
https://addons.mozilla.org/en-US/fir...ullzoom-level/
Tiny space on the main toolbar that also displays the zoom %