Mozilla offers sysadmins a Policy Engine for roll-your-own Firefox installs

And warms to a kind of speculative execution for Tabs, too. Really.

By Simon Sharwood


Mozilla’s announced it will add a “policy engine” to the next extended support (ESR) release of its Firefox browser.

ESRs are supported for at least a year and give users the chance to settle on a browser for a while, rather than having to keep up with the faster release cadence offered to consumers. The next ESR release will be Firefox 60, scheduled to emerge on May 8th, 2018.

It’s a notable release for a couple of reasons. Firstly, it will be the first ESR to incorporate Firefox 57, aka “Quantum”, the re-write of the browser introduced in November 2017. It will also add a policy engine that lets users roll-their-own versions of Firefox.

Documentation for the feature is scanty, but Mozillans have so far suggested it will involve a JSON file to be deployed with the browser and which allows controls such as:

Firefox developers have also pondered a new feature called “Tab warming” that will start loading the contents of a Tab as soon as a user hovers over it.

The Quantum of Firefox: Why is this one unlike any other Firefox?


“When you switch a tab in multi-process Firefox, traditionally we’d send a message to the content process to tell it to paint its layers, and then we’d wait for the compositor to tell us that it had received those layers before finally doing the tab switch,” wrote Firefox developer Mike Conley, who said that method works pretty well but added “I think we can do slightly better.”

Tab warming will therefore watch as your mouse approaches a closed Tab and, once Firefox is almost certain you want to open it, will start loading some layers in the background. Conley said that users won’t notice a difference on most pages, but that a few will on a few pages and that’s enough reason to make the effort.

He also promised that if a user chooses not to load the tab, Firefox will throw away anything it loaded in advance.

Let’s hope he and other Mozillans get that right, seeing as trying to guess what users want in memory has gone so very, very, well lately. ®

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