Bug 1772945 - Enable "css-masonry" feature for Thunderbird. r=Gijs,pr…

…eferences-reviewers

The new address book layout in Thunderbird 102 uses masonry layout.
The UI team has requested that the feature be turned on as another
approach would not work as well due to the dynamic and modular
nature of the new UI.

Differential Revision: https://phabricator.services.mozilla.com/D148451

toolkit/components/featuregates/Features.toml

@@ -7,7 +7,7 @@ preference = "layout.css.grid-template-masonry-value.enabled"
 type = "boolean"
 bug-numbers = [1607954]
 is-public = true
-default-value = {default = false, nightly = true}
+default-value = {default = false, nightly = true, thunderbird = true}
 
 [web-api-webgpu]
 title = "experimental-features-web-gpu2"