1808726 - Avoid gBrowser.visibleTabs in _mouseenter()

Status: RESOLVED WORKSFORME

(Firefox :: Tabbed Browser, task)

Description

[Oriol Brufau [:Oriol]]

gBrowser.visibleTabs is slow when there are lots of tabs.

If e.g. a thousand of tabs are removed, _setPositionalAttributes() will be called lots of times, and if the user is hovering a tab, it will keep calling _mouseenter().

Comment 1

[Oriol Brufau [:Oriol]]

Attachment: Bug 1808726 - Avoid slow gBrowser.visibleTabs in _mouseenter(). r?Gijs

This patch won't improve performance by itself, since visibleTabs will
have been likely computed and cached in _setPositionalAttributes, but
it's the first step towards avoiding that work in hot code paths.

Note that previousVisibleTab and nextVisibleTab are not cached, so on
the worst case they may keep iterating several hidden tabs, but I think
it's fine given that most tabs are probably visible, and a cache may be
considered in the future. Also note that existing code was using linear
indexOf which wasn't great either.

Comment 2

[Oriol Brufau [:Oriol]]

This is already covered by https://phabricator.services.mozilla.com/D166094 from bug 1808661.