Icon for dark theme about undoclosetab

[M-Reimer]

Thanks for reporting.
I've filed a bug for this: https://bugzilla.mozilla.org/show_bug.cgi?id=1405026
I currently don't know of any way to get info about the loaded theme.

[KwanEsq]

As long as your icon is static the currently undocumented browser_action.theme_icon key of the manifest should do what you want (especially once https://bugzilla.mozilla.org/show_bug.cgi?id=1404568 lands)
Some in-tree doc here: https://hg.mozilla.org/mozilla-central/file/613f64109bde/toolkit/components/extensions/schemas/manifest.json#l352
basically add

"theme_icons": [{
  "dark": "icons/undoclosetab.svg",
  "light": "icons/undoclosetab-light.svg",
  "size": 19
}]

to browser_action

[M-Reimer]

You are right, but the discussion in https://bugzilla.mozilla.org/show_bug.cgi?id=1394579#c20 suggests, that there may be a better API in future.
The API, you found, is better than nothing, so I'll have a look at this and ship the next version with two SVG icons.

[M-Reimer]

See:
ff5962f
I'll leave this bug open for now, waiting for the resolution of https://bugzilla.mozilla.org/show_bug.cgi?id=1394579#c20
But I can live with the current solution. The second icon is autogenerated by just replacing the "dark" color with white automatically.

[MatMoul]

I think this API can reply to this issue :
https://developer.mozilla.org/fr/Add-ons/WebExtensions/API/browserAction/setIcon

[M-Reimer]

The keys, suggested by @KwanEsq are now officially documented:
https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/browser_action
So I guess we won't see anything better in the near future.
As I already use this since a few versions, I'll close this issue now.