Reproducible: always

Steps To reproduce:

1. Right mousedown on empty space of content area
2. Keeping mousedown, move mouse pointer to tab
3. Then, mouseup

Actual Results:
Some TabContextMenu items are blank label

Expected Results:
No blank label

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a1cfb4874e277b523330f3595ac138897b49f41a&tochange=028c0eff90a7ad121827f45040699bbca433c5e7

Regressed by:
028c0eff90a7ad121827f45040699bbca433c5e7 Brian — Bug 1523763 - Move tab context menu strings to FTL file loaded on-demand. r=Gijs,flod

Gijs, thoughts on how to address this?

I think we have a few options:

1. detect mousemoves/mouseovers as well, which is a little sad-making, perhaps, from a perf perspective
2. add fallback in onpopupshowing or oncontextmenu, which might cause a flash of unlocalized content, I guess?
3. move from mousedown to mouseup on windows (and/or linux? mac context menus appear onmousedown...) and/or use both
4. add some kind of complicated helper that intercepts an initial context menu showing, cancels it, and then re-opens it when l10n is ready

I'd be inclined to go for 2 or 3, but I'd like a second opinion. Jared, Dão, what do you think?

Can we add a capturing {once: true} mousedown event listener on the whole window and just initialize on that?

(In reply to Jared Wein [:jaws] (please needinfo? me) from comment #3)

Can we add a capturing {once: true} mousedown event listener on the whole window and just initialize on that?

Apparently I was confused and we already have a mouseover listener? I don't know off-hand why that wouldn't fire in the steps in comment #0...

The mouseover listener is only on the tabContainer. I assume holding down the right mousebutton while dragging it skips the mouseover event.

https://hg.mozilla.org/mozilla-central/rev/92923a205734

Should we uplift this to 68?

Alice, can you confirm this is fixed for you?

Yes. It was fixed!.
No longer reproduced on latest Nightly69.0a1.
Build ID 20190603101337
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0

Comment on attachment 9069059 [details]
Bug 1555453 - use contextmenu event as backup to ensure we always localize the context menu, r?jaws

Beta/Release Uplift Approval Request

• User impact if declined: Broken context menu in some cases
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: n/a
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Very small frontend-only patch, still got lots of beta runway.
• String changes made/needed: nope

Marking verified per comment #11 - thanks Alice!

Comment on attachment 9069059 [details]
Bug 1555453 - use contextmenu event as backup to ensure we always localize the context menu, r?jaws

approved for 68.0b8

https://hg.mozilla.org/releases/mozilla-beta/rev/836d74518ab6