Update security slider to take JIT preference changes into account
For a while there were different JIT prefs for content and chrome. That changed with bug 939562. We need to adapt the slider to reflect that.
Suggested prefs for disabling now are
javascript.options.ion
javascript.options.baselinejit
javascript.options.native_regexpasm.js is already off due to other reasons (#19417 (moved))
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information