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Embedding preferences

nsIPrefService provides enable/disable and settings functionality for mozilla. Below are *some* prefs that are used to control various settings that may be pertinent to embedding scenarios. If you have other's please let me know . These are not public yet so use at your own risk.

CAPS (capabilities/privileges)

You can control JS access/privileges using these prefs. See for more info. See Mitch Stoltz regarding questions/concerns/suggestions in this area.

Name Value Type Changeable at runtime
javascript.enabled boolean yes
capability.policy.strict.sites string (space delimited list of urls) yes string (example: "noAccess") yes
capability.principal.default.htmlinputelement.value string (example: "sameOrigin") yes string (example: "sameOrigin") yes string (example: "UniversalPreferencesRead") yes


There are a number of settings that are useful for accessibility.

Name Value Type Changeable at runtime
network.image.imageBehavior int (0=Accept, 1=Accept images from originating server only, 2=no images) yes
network.cookie.cookieBehavior int (0=Accept, 1=Accept cookies from originating server only, 2=no cookies) yes
browser.display.foreground_color string, hex color value (like #abcdef) yes
browser.display.background_color string, hex color value (like #abcdef) yes
browser.display.use_system_colors boolean yes
browser.display.use_document_colors boolean (if false, prevents background images from loading) yes
browser.anchor_color string, hex color value (like #abcdef) yes
browser.visited_color string, hex color value (like #abcdef) yes
image.animation_mode string, "normal", "none" or "once" yes

User Agent

You can modify the User Agent string sent out in HTTP requests. See for usage of each piece. Generally, the ".misc" field is used by people to "tag" the UA w/ their grafitti.

Name Value Type Changeable at runtime
general.useragent.locale string (a chrome:// url pointing to a properties file) unknown
general.useragent.misc string (example: "m18") unknown
general.useragent.override string (a string to completely override the UA string) unknown
general.useragent.vendor string
general.useragent.vendorSub string
general.useragent.vendorComment string
general.useragent.product string
general.useragent.productSub string
general.useragent.productComment string
general.useragent.misc string string


For other i18n charsets, change x-western in the preference name to x-central-euro, x-cyrillic, x-unicode, x-user-def, x-baltic, el, tr, he, ar, th, ja, zh-CN or zh-TW.

Name Value Type Changeable at runtime string yes string yes string yes
font.default string "serif" or "sans-serif" yes
browser.use_document_fonts int, 0=no, 1=yes yes