Fix #243: Serve vendor favicons locally instead of remotely.

[Osmose]

Tracking protection is blocking the eBay favicon from being loaded in private
browsing mode, but serving it locally instead of fetching it from the internet
avoids being blocked.

[biancadanforth]

R+!

It is curious that Ebay's favicon is blocked, when Amazon's is not, while both ebay.com and amazon.com are on the Disconnect blocklist that is the basis for Tracking Protection. @groovecoder , any idea why that would be?

Thinking about the future, if we ever were to open the extension to all sites (or a really large number of sites), would we want to use nsIFaviconService as mythmon suggested in PR #207 ? In general, how might we fix this if we were supporting * for our allowList pref?

[groovecoder]

Looks like amazon.com is in the Content category, alexametrics.com is in the Analytics category, while domains like amazon-adsystem.com are in Advertising. So, amazon.com isn't in the default TP list for PBM. (default TP list for PBM doesn't include Content category)

ebay.com is in the Advertising category, so it's in the default TP list for PBM.

Good change, regardless. Disconnect may not have categorized amazon.com as a tracking domain, but reducing 3rd party requests is always great.

[Osmose]

Thinking about the future, if we ever were to open the extension to all sites (or a really large number of sites), would we want to use nsIFaviconService as mythmon suggested in PR #207 ? In general, how might we fix this if we were supporting * for our allowList pref?

That's one way, and probably the way we want. There's also JS libraries that claim to be able to fetch the favicon for a webpage, or we assume that favicons are at domain.com/favicon.ico and only support that. But those seem worse than using the favicon service.