The last 4 versions of Firefox, ending in 55.0.2, has had zoom feature working on/off. Counting backwards as I did not write down the version before, I just get them through Xubuntu 14.04 LTS 32bit(I don't use windows at all) software updater: 55.0.2 - zoom not working - will only work if 3rd party addon is installed. previous Firefox - zoom worked like a charm without 3rd party addon. previous Firefox - zoom not working - will only work if 3rd party addon is installed. previous Firefox - zoom worked like a charm without 3rd party addon. I don't know if it has been in other versions this year, but it has happened in the past on different systems, with either linux or windows(7 and 10) and different owners. Basically there is an update and then zoom don't work (which is very strange as zoom is a build-in function since Firefox version 3) - then there is a new update and zoom works again - then a new update and zoom don't work again - and it continues. I think you need to look at what is happening and why this happens - and then issue an update. Kinda stupid that build-in function gets disabled every second update. I know I can install an addon which gives me the feature, but then I could continue doing that everytime "someone" "forgets" a function in the newest update - better get it sorted out now. In the meantime I use Zoom page WE(but its clutter, I could live without). A page in the support section on how to disable/enable build-in functions through about:config would be nice. And to keep it updated if major changes are made. You have some very old guides still there, going back to firefox 3, they do not apply to firefox 55. Hope this will be fixed soon. JBJ