Option/Alt + click opens a link in split view

[chirivelli]

Option/Alt + click on a link now opens it in a split with the current tab, analogous to Glance’s modifier-click.

Collision check

This can be done, with one real overlap:

• Glance (default trigger is Alt + click). If Glance is enabled and its trigger is still Alt, Glance keeps Option/Alt + click. Split only uses that gesture when Glance is off or bound to something else (Shift, Ctrl, Meta). That matches the “Shift + click = Glance, Option + click = split” setup.
• Firefox Alt + click save. When this feature handles the click it preventDefaults, so it replaces save-link-as for that gesture. Disable with zen.splitView.alt-click-open.
• Alt + click on a tab (zen.splitView.enable-tab-click-split) is unchanged; that only applies to the tab strip, not in-page links.
• Cmd/Ctrl + click (new tab) and Shift + click (Glance, if configured) are not used.

Behavior

• Option/Alt + click a link → new tab split with the current tab (same path as “Split link” in the context menu).
• Same gesture on a bookmark, unless Glance claims the modifier.
• If the current split already has 4 tabs, the link still opens and the existing limit toast is shown.

Pref

zen.splitView.alt-click-open (default true).

Tests: src/zen/tests/split_view/browser_split_view_alt_click.js.