A story of bug fixing

9 April, 2016 § Leave a comment

I spent some time last night looking in to a bug in the Firefox preferences as part of the Outreachy internship I’m mentoring. This bug is about how the context menus in our preferences were squished horizontally compared to normal context menus. I’ve put screenshots of the two below so you can compare.


Looking at bug 1247214, I knew that context menus outside of the preferences looked fine but context menus in the preferences were broken. This meant I had something I could compare side-by-side when looking at the CSS.

I used the inspector and looked at the applied styles for a xul:menuitem and compared them between the preferences and non-preferences. I was surprised to see that they were nearly identical, and what differed was inconsequential.

After walking up the DOM from the xul:menuitem and seeing that the two instances were still nearly identical, I had to think of a different route. Somewhat by chance I realized/remembered that there were children nodes of the xul:menuitem that could possibly be affected. In the Inspector I expanded the xul:menuitem and looked at the rules for the xul:label inside of it. Immediately I noticed that the -moz-margin-start and -moz-margin-end were being set to zero and the rule looked like it wasn’t intended to affect context menus. Unsetting that rule fixed the bug.

So that describes how I found the issue with the bug. Figuring out a fix for it wouldn’t be that difficult now. I also wanted to find what changeset introduced the bug so I could learn more about why it was there.

Using MXR, I pulled up the `hg blame` for the file and went to the offending line. Clicking on the revision number on the left of the line brings up some of the diff from the changeset. At the top of this new page, I clicked on “changeset” to see the full changeset. This unfortunately was a refactoring changeset and wasn’t what actually introduced the offending lines. I then clicked on the parent changeset and based off of that revision found the file again and ran `hg blame` on it. Now the offending line was linked to the changeset that introduced the bug.

After reading through the bug that introduced the changeset I knew that I could safely make this change as the lines were never intended to alter context menus, and I also knew what to look for and test while making the change so I wouldn’t regress the original bugfix.

All of this being said, I probably could have found this quite a bit faster by using a tool called mozregression. mozregression is a tool that will help you run a binary search on all of our nightly builds (continuous integration ones too). As you are likely already aware, binary search is very fast, letting mozregression help narrow down the day that the regression got introduced from a range of 10 years to a single day in about 7 builds.

If I had taken the mozregression route I probably could have saved myself about 45 minutes of debugging and digging around. But both routes work well, and sometimes I learn more from one than the other.

I know this write-up was long, but I hope it was valuable.

Final In-content Preferences status update

6 May, 2015 § Leave a comment



We are now a week away from the release of Firefox 38, and with it will finally come the release of in-content preferences. You can download Firefox Beta today to see what it will look like when it hits Release next week.

I want to give a huge thanks to all of the people who worked on the project. You all helped it get to the point where hundreds of millions of people will get to see a refreshed and modern preference experience.

Major thanks goes out to Stephen Horlander, Michael Maslaney, Madhava Enros, Gijs Kruitbosch, Blair McBride, Richard Marti, Tim Nguyen, Justin Dolske, Zhenshuo Fang, Dão Gottwald, Tim Taubert, Matthew Noorenberghe and a huge host of other people that have helped.

Known issues:
1) Dialogs opened in the Advanced pane don’t use the same tab-modal dialog implementation that can be found within the rest of the preferences. We hope to get this fixed in a future release very soon.
2) The design for focus rings within the preferences still has a refresh coming, but it won’t make Firefox 38. As with #1, we hope to get this in to a future release very soon.
3) If you have gone to about:config and set browser.search.showOneOffButtons to `false`, the Search pane of the preferences is broken. The fix for this didn’t make the 38.0 cut-off, but it will be fixed within the next few weeks following release. Going forward this preference will be removed, so now may be a good time to revert that preference back to `true`.

Other lower-impact known issues can be found on Bugzilla.

You can download Firefox Beta today to see what it will look like when it hits Release next week.

Status update – In-content Preferences, part 5

4 March, 2015 § 4 Comments


Firefox 38 has now merged to Aurora (Firefox Developer Edition) and we are a couple weeks into development of Firefox 39 on mozilla-central. At this point, bugs that are fixed on mozilla-central will need to be uplifted to mozilla-aurora to continue to ride the 38 train.

These are some of the 21 bugs that were fixed since the last update (1/31/2015):

  • Bug 1008171 No focus for elements except textboxes (and buttons, on Windows and Linux) inside in-content preferences
  • Bug 1025719 – openPreferences(panelName) doesn’t open the requested pane if about:preferences is in a yet-to-be-loaded tab
  • Bug 1034296 – Action dropdown in Application pane does not open when session restored
  • Bug 1037225 – Consider keeping browser.preferences.instantApply = false on Windows
  • Bug 1044597 – in-content preferences: resized dialogs should not push buttons into overflow
  • Bug 1047586 – Unable to interact with in-content preferences after changing minimum font size to a very large value
  • Bug 1108302 – Menulists in the in-content preferences have too much padding at the start of their contents
  • Bug 1111353 – No longer displayed check mark in in-content preferences if Text : white, Background : Black and Select “Never” in “Content” > “Colors…” > “Allow pages to choose their own colors, instead of my selections above”

Since the last update all of the P1-tracked bugs have been fixed. We are tracking the following P2 bugs:
top_2Bug 1043612 – Persist the size of resizable in-content subdialogs
top_2Bug 1136645 – InContent prefs – Make focusrings match the spec on Windows and Linux
top_2Bug 1044600 – in-content preferences: empty dialogs after pressing backspace or the Back button

Bug 1044600 in the above list should be very close to getting fixed. It has landed and been backed out a couple times due to intermittent failures and leaks, but is making steady progress towards being fixed.

Gijs and I will be meeting up in less than two weeks in San Francisco to have a “hack week” focusing on the in-content preferences. We’ve gone through the list of bugs in the in-content preferences and put together a subset of 10 bugs that we’ll tackle during the week if they’re not fixed beforehand.

Big thanks go out to Ian Moody [:Kwan], Gijs, Yash Mehrotra, Richard Marti [:Paenglab], and Tim Nguyen [:ntim] for their help in fixing the 21 bugs.

Status update – In-content Preferences, part 4

31 January, 2015 § 1 Comment


We are now about half-way through the normal development cycle of Firefox 38. In about 3-4 weeks, what is currently “Nightly 38” will become “Firefox Developer Edition 38” (previously known as Firefox Aurora). At this point, beta builds of Firefox 36 will now revert back to the old-school preferences implementation. Firefox Beta will see the in-content preferences get more testing at the beginning of the Beta 37 iteration.

These are some of the bugs that have been fixed since the last update:
Bug 1022582 – Checkboxes and radio buttons in about:preferences lack any indication they’re checked/selected when using High Contrast mode
Bug 1043346 – InContent Prefs – Dialogs should have their dimensions reset after closing
Bug 1008172 – Scrolling up and down on pages with scrollbars in about:preferences will change subgroups (the Advanced subpanes)
Bug 1012223 – in-content preferences loading slowly

I’ve gone through the remaining bugs and attached both a “point” value as well as priorities for the bugs. Point values follow the Fibonacci sequence, and should roughly approximate the difficulty of fixing the bug. Priorities range from P1 to P3.

P1 bugs are considered those that block using the feature, as well as those that are highly visible. We are tracking three P1 bugs:
top_1Bug 1108302 – Font size select list shows ellipsis instead of selected value (points = 1)
top_1Bug 1044597 – in-content preferences: resized dialogs should not push buttons into overflow (points = 3)
top_1Bug 1047586 – Unable to interact with In-content preferences after changing Font size (points = 5)

The full list of bugs can be found on Bugzilla.

Big thanks to Richard Marti, Shubham Jindal, and Gijs Kruitbosch for helping to fix the previously-mentioned bugs.

Status Update – In-content Preferences, part 3

10 December, 2014 § 2 Comments


Since the last update, bug 1022582 (checkboxes and radio buttons in about:preferences lack any indication they’re checked/selected when using High Contrast mode) has been marked ready for check-in and should be marked fixed by late tomorrow.

This marks the last of the high-contrast bugs blocking the release 🙂

We also have had great progress on bug 1043346 (dialogs should have their dimensions reset after closing). This bug looks ready to land after the patch gets updated.

I’m optimistic that we can get a fix in for bug 1008172 ([linux-only] scrolling up and down on pages with scrollbars in about:preferences will change subgroups) soon. I put some tips in the bug, and Richard Marti has said that he will try to take a look at it.

As for bug 1056478 (resizer of sub-dialog follows only half of the movement of mouse pointer), I’m not sure if we should keep it as a blocker. This bug reveals an underlying issue in Gecko (bug 1105906) that exists with any centered resizable element. Webkit doesn’t suffer from this issue, so it’s hopeful that we will find a solution, but I don’t know if this quirk should stop us from shipping.

The next bugs that I would like to see attention on are:
Bug 1043612: Persist the size of resizable in-content subdialogs
Bug 1044597: in-content preferences: resized dialogs should not push buttons into overflow
Bug 1044600: in-content preferences: empty dialogs after pressing backspace or the Back button

All three of these bugs are part of the subdialogs category. Thanks for the work to those contributing patches and helping test, we couldn’t do this without you! 🙂

The Bugs Blocking In-Content Prefs, part 2

26 November, 2014 § 1 Comment

Season's greetingsAt the beginning of November I published a blog post with the list of bugs that are blocking in-content prefs from shipping. Since that post, quite a few bugs have been fixed and we figured out an approach for fixing most of the high-contrast bugs.

As in the last post, bugs that should be easy to fix for a newcomer are highlighted in yellow.

Here is the new list of bugs that are blocking the release:

The list is now down to 16 bugs (from 20). In the meantime, the following bugs have been fixed:

  • Bug 1022578: Can’t tell what category is selected in about:preferences when using High Contrast mode
  • Bug 1022579: Help buttons in about:preferences have no icon when using High Contrast mode
  • Bug 1012410: Can’t close in-content cookie exceptions dialog
  • Bug 1089812: Implement updated In-content pref secondary dialogs

Big thanks goes out to Richard Marti and Tim Nguyen for fixing the above mentioned bugs as well as their continued focus on helping to bring the In-Content Preferences to to the Beta and Release channels.

The Bugs Blocking In-Content Prefs

6 November, 2014 § Leave a comment

Paper Firefox!If you’ve been following my blog, you know that there has been a long on-going project to rewrite Firefox’ preferences and move them to a page within the browser.

Work has continued on that front, but it has been moving at a slow pace. Today, representatives from engineering, user experience, and project management met together to form the remaining list of bugs that are blocking us from shipping in-content preferences to the Release channel.

In total, we have 20 bugs blocking the release. There are five different categories that the bugs fit in. Bugs that should be easy to pick up and finish for a new-comer are highlighted.

If you’d like to work on one of the above bugs, please click on the bug and read the details. If you have any questions, please post the question in the bug and someone will get back to you. Thanks!

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