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Jancy

Preference Sets

Preference sets let you declare alternate values for certain settings that influence how tabs are created.

Sets

This dropdown displays your currently defined preference sets.

Delete

Delete the current selected preference set.

Rename

Rename the currently selected preference set.

New

Create a new preference set.

Core Settings

Start with audio muted

If checked, tabs will start muted.

Start with images enabled

If checked, tabs will start with images enabled.

Enable background throttling

Controls if tabs consume less resources when they don’t have focus.

This feature can potentially affect the following things in the page:

  • animations
  • timers (which could inclue the timers the capture cart timers and queue positions)
  • Page Visibility API which is the technology used by websites to know if the tab has focus or not

In testing we noticed a perceivable difference in how frequently things such as queue positions updated when running 40+ tabs. Your mileage may vary.

Superfast domain name parsing

If checked, a shortcut will be used to parse domain names from URLs on every outgoing request and on some incomming responses. If unchecked, all URLs will be fully parsed and just the domain name will be used.

In testing, the superfast domain name parser seems to be fine. Fully parsing every URL and just using the domain name for the problem Jancy is trying to solve is overkill but the shortcut that the superfast domain name parser uses might not work in every situation.

Allow websites to read the system clipboard

If checked, a website will be allowed to read the systems’ clipboard.

Disable WebAuth for websites

If checked, disable a websites ability to use the WebAuth APIs.

Run tabs in preloader compatibility mode

If checked, preloaders that don’t conform to Jancy’s newer preloader spec and no longer work will continue to work.

Turning this option on will potentially increase the likelihood that the renderer processes in tabs will crash more frequently.

Generate a unique canvas hash per partition

If checked, each tab belonging to the same partition (ie. related tabs) will generate a unique canvas hash that might help with sites that check for uniqueness of canvas hash values.

In v1.12.0 we added the ability to select how the canvas hash is generated.

  • method 1
  • method 2
  • both method 1 and method 2

The two methods we came up with to implement this feature are secret sauce on our part. Both methods (or the combination of methods) results in the generation of a unique canvas hash for the sites we used in testing. The reason there are two methods is because method 1 worked well on one site we tested against but method 2 was being detected. Unfortunately, the opposite held true for a different site we use for testing.

Tab V8 caching option

Controls the v8 code caching policy used by Chromium.

  • disable code caching turns off code caching all together
  • heuristic based code caching
  • bypass code caching heuristics but with lazy compilation bypasses code caching heuristics but with lazy compilation
  • bypass code caching heuristics but with eager compilation same as above except compilation is eager

I think disabling code caching make the most sense. Since all Jancy sessions exist only in memory, any cached code would only be saved to the in-memory cache and discarded when the session goes away. Furthermore, since tabs are isolated and don’t share sessions, the cached code wouldn’t be shared amongst tabs all visiting the same website. By disabling the code caching your in-memory overhead should be lower becasue you’re not paying a tax to cache code you’re just going to discard. I haven’t done extensive testing on this so I might be wrong in some assumptions I’ve made. More info can be found here.

Tab WebRTC handling policy

  • disable non proxied udp does not expose public or local IPs. When this policy is used, WebRTC should only use TCP to contact peers or servers unless the proxy server supports UDP.
  • default public interface only exposes user’s public IP, but does not expose user’s local IP. When this policy is used, WebRTC should only use the default route used by http. This doesn’t expose any local addresses.
  • default public and private interfaces exposes user’s public and local IPs. When this policy is used, WebRTC should only use the default route used by http. This also exposes the associated default private address. Default route is the route chosen by the OS on a multi-homed endpoint.
  • default exposes public and local IPs. This is the default behavior. When this policy is used, WebRTC has the right to enumerate all interfaces and bind them to discover public interfaces.

Bypass CORS for requests to these URLs (separate multiple URLs with a semicolon)

A semicolon delimited list of URLs that if the destination of an outgoing request matches against, CORS will be disabled for.