If you use firefox, and zoom whilst on a particular site, firefox tries to remember that setting for that site, so it should always open at the same magnification.

Aurora Channel
I note you are using the Aurora channel, you may note there are also the Beta and Release channels available.
(The easiest method of changing channel is to download and install the relevant Beta or Firefox release version, but do NOT take any option to delete personal settings; because that removes all profiles from all normally installed versions of Firefox, and you will loose pass words bookmarks etc)

• see Beta & Aurora
• Current Release

The Firefox Page Zoom feature does a domain by domain level of saving the users preferred zoom level settings, there is no default Page Zoom level setting in Firefox, as with some other browsers.

Try the Default FullZoom Level extension:
https://addons.mozilla.org/en-US/firefox/addon/6965

Or the NoSquint extension:
https://addons.mozilla.org/en-US/firefox/addon/2592/