Photon Engineering Newsletter #4

Welcome to Photon update #4! [Yes, another update this week. I’ve caught up with the backlog, so these updates should now reflect recent work over the last 7-10 days.]

Let’s first talk about a couple of projects that overlap with Photon and have led to some questions about how things fit together.

Quantum Flow and Photon

Quantum Flow is a project to find and prioritize fixing performance issues across the browser. We’ve found and/or fixed hundreds of bugs so far, tagged “[qf:p1]” in Bugzilla. Photon is a project to refresh Firefox’s UI, which also has a major performance component. Photon also has a big bug tree of front-end performance issues found and/or fixed.

So, hey, are these separate projects? Are we duplicating effort? The answer is “no” to both.

Quantum Flow started off with an emphasis on platform bugs, since web content performance is, y’know, a pretty important consideration for a web browser. The Photon project got rolling well after Quantum Flow had begun, and is simply the front-end complement to Quantum Flow’s performance investigations. The two projects are basically just different views into the same underlying work, and are coordinating very closely.

The Photon performance work is a little more structured than Quantum Flow as a whole, though. We’ve clustered the front-end performance bugs into about 10 areas of specific types of bugs or UX interactions. These are not the only areas of front-end performance, but are the ones  we want to focus on for around the Firefox 57 timeframe.

Photon Mobile

The main focus of Quantum and Photon is Desktop Firefox. However, the mobile team will be doing a visual refresh of Firefox on iOS and Android to fit in with the new Photon design. They’ll be updating iconography and colors, as well as making the page loading indicators, menus, toolbars, and tab tray more consistent across iOS and Android. It’s also worth noting that Firefox on Android will still benefit from some of the Quantum improvements, since it’s also built on top of Gecko (on iOS we use WebKit, due to Apple’s platform restrictions).

Recent Changes

Here’s what’s happened in Photon this week.
  • Page action menu is taking shape – now has “Send to device” and bookmarking functionality. Pocket functionality is next on the list.
  • Long overdue maintenance and performance improvement work on panels, panelmultiviews and their transitions is ongoing, getting better every day.
  • Customization context menus and customize mode improvements have landed – customize mode is now more usable when the photon pref is toggled. We’re getting closer to toggling that pref on nightly.
  • Sidebar switcher improvements have landed. You can now move the sidebar to the left or right side, WebExtension sidebars are now listed, and some styling improvements have been made. When the sidebar button has also been updated this part of the project will be nearly done.
  • Initial patches for the new Library panel are awaiting review.


  • Work continues on animations for downloads toolbar button, stop/reload button, and page loading indicator – but these haven’t landed yet.
  • Looked into SVG spritesheet production+optimization with SVGO plugins. This allows us to both to cleanup the SVG markup and optimize out some of the poor SVG generated by graphics editors.
  • We’ve decided to hold back the preferences reorg until Firefox 56. As previously noted, we’re planning on making some further revisions to the preferences reorg that has already landed in Nightly. They’re not large in scope, but 55 goes to Beta in just a few weeks (June 12th), and we want to make sure we get things right before shipping it to Beta or Release.
  • Updated the strings in the new performance page, added a search icon to the search field, and fixed a number of other small bugs.
Visual redesign:
  • The title bar is now dark by default on Windows 10. It’s a pretty striking look, and we think you’ll like it. A similar change for OS X is coming.
    The dark purple has led to at least one interesting reaction. 😉
    Screen Shot 2017-05-30 at 3.14.49 PM
  • The arrow in the back button got a bit smaller. This makes it consistent with the forward arrow – which is especially important for use in Compact Mode, where both are styled identically (i.e. no circle around the back button).
  • Windows 7 no longer has a custom toolbar background color. It was bluish, and is now just a normal grey.
  • Started to remove the “compact” from the “compact light/dark” themes that shipped in Firefox 53. Wait, wait. Hold your fury! With Photon, “compact” will simply be a mode independent of any particular theme. You’ll still be able to have a compact-dark theme. But can also have the default theme be compact, or have a non-compact dark theme. Or use a 3rd party theme in compact mode.
  • Removed dropdown markers for bookmark folders and toolbar buttons.
  • Coordinating with the Activity Stream project to finalize automigration UI. Also discussing impact to the onboarding tour, as Activity Stream will only be doing a limited rollout (5% of users) in Firefox 56. Adapting the tour to the current (pre-Activity Stream) about:home and New Tab page introduces some complications and extra work.
  • Completed a User Research study to better understand why users download Firefox and what their expectations are.


  • Even more sync reflow tests are being written, as well as a test to list files loaded early during startup. These help ensure we don’t regress the fantastic performance improvements that have been made so far.
  • We got some nice contributions, especially a couple fixes from Dão for sync reflows in tab interactions.
  • The last thing causing NSS initialization before first paint is captive portal detection, and should be fixed soon.
  • Felipe Gomes is joining the Photon Performance team, and will focus initially on jank caused by code running off of timers. He’ll have an intern starting soon who we expect will start by fixing some main thread IO bugs. Also, the rest of the Photon team will be starting to use some of their time to begin working on other performance bugs.


End of transmission.

3 thoughts on “Photon Engineering Newsletter #4”

  1. Can you combine the Firefox Share button into the action page button? You can add a QR code to it. I think we should switch three horizontal dots to three vertical dots or switch this icon into the icon of the Firefox Share button.

    1. We’re not currently planning on integrating Firefox Share into this button (it will continue to exist as an optional, independent button). We’ll try to revisit this in the future, but there are some complications with doing this that prevent us from tackling it for 57.

      1. yeh. What do you think about idea switch page action button from three horizontal dots to three vertical dots?

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