1751843 - accessibility.mouse_focuses_formcontrol = 0 spontaneously breaks throughout all browsers in a chrome window

Status: NEW

(Core :: DOM: UI Events & Focus Handling, defect)

Description

[Shane Hughes [:aminomancer]]

I don't know exactly how to reproduce this, but I do have a video of it. And it's currently affecting one of my windows so if anyone can think of any tests to run before I need to restart Firefox, let me know.

Basically I have accessibility.mouse_focuses_formcontrol set to 0, because I'm just not a fan of the 1px dotted focus outlines. So clicking an anchor element should not focus it. And normally it doesn't. But when I'm using Firefox it will sometimes spontaneously break, always focusing form elements on click, and remain like that until I close the window or quit Firefox. It applies universally within that window, including in webextension panel and sidebar documents. But if I open a new window, that one won't have the same problem, or at least not immediately.

In my video you can see a scenario where my main window is suffering from the bug, so I restore one of the browsers into a new window by dragging the tab out of the scrollbox. And now the bug isn't present. Strangely, if I drag the tab back into the main window, the bug does not return in that particular browser. But it does persist in all new browsers opened in that window.

This generally doesn't happen very often, so I haven't taken much notice of it. Maybe once a week, and then only if I let Firefox run without restarting for more than a day. It does not seem to be associated with any error or console message, nor with any other bug I can discern. It doesn't seem to affect buttons or images. I'm not sure what else it may affect, but I've only seen it happen on anchor, video, and audio elements.

I imagine this will be pretty difficult to track down since it's so hard to reproduce at will. But figured there should be a record of this, in case anyone else can corroborate

Comment 1

[Shane Hughes [:aminomancer]]

Attachment: A video of the bug, where anchors are focused on mousedown despite the pref disabling this

Here's a recording. To be clear, the pref has been set to 0 in this profile for years. So it was active at app startup. I guess I just toggled it in the video for dramatic effect lol

Comment 2

[Hsin-Yi Tsai (she/her) [:hsinyi]]

Please feel free to let me know if we should raise the severity level.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

So I'm confused because that pref doesn't affect <a> elements to begin with (https://searchfox.org/mozilla-central/search?q=symbol:_ZNK20nsGenericHTMLElement29IsFormControlDefaultFocusableEb&redirect=false)

That pref shouldn't be needed fwiw. Focus rings shouldn't be shown even when form controls are focused unless they're focused via the keyboard. The only thing that should cause focus rings to always be set is some Windows stuff that causes this to return true:

https://searchfox.org/mozilla-central/rev/66e59131c1c76fe486424dc37f0a8a399ca874d4/widget/windows/nsWindow.cpp#6121-6141

But I'm not familiar enough with Windows to know when that code is triggered.