Bugzilla

I confirmed also that the situation is similar for the font list in about:preferences: it's a XUL <menulist> element rather than a <select>, but it also builds a XUL scroll frame which is rendered in a popup. So, if we enable APZ in popups, that should start scrolling with APZ as well.

Note that the current pref `apz.popups.enabled` only enables APZ in popups [with remote content](https://searchfox.org/mozilla-central/rev/867cbb1a2b232398616e1aa42f913f37c6cb38e4/widget/nsBaseWidget.cpp#861), which doesn't apply to either <select> or <menulist>. Popups without remote content don't even use OMTC, which is a preprequisite for APZ.

I discussed this briefly with Jeff. We wouldn't want to blanket-enable OMTC+APZ for all popups, since that would include things like tooltips and OMTC+APZ is a bit heavyweight for a tooltip. However, it may be reasonable to enable them for popups which actually have scrollable content, such as the <select> and <menulist> popups.

I confirmed also that the situation is similar for the font list in about:preferences: it's a XUL <menulist> element rather than a <select>, but it also builds a XUL scroll frame which is rendered in a popup. So, if we enable APZ in popups, that should start scrolling with APZ as well.

Note that the current pref `apz.popups.enabled` only enables APZ in popups [with remote content](https://searchfox.org/mozilla-central/rev/867cbb1a2b232398616e1aa42f913f37c6cb38e4/widget/nsBaseWidget.cpp#861), which doesn't apply to either <select> or <menulist>. Popups without remote content don't even use OMTC (off-main-thread compositing), which is a preprequisite for APZ.

I discussed this briefly with Jeff. We wouldn't want to blanket-enable OMTC+APZ for all popups, since that would include things like tooltips and OMTC+APZ is a bit heavyweight for a tooltip. However, it may be reasonable to enable them for popups which actually have scrollable content, such as the <select> and <menulist> popups.

I confirmed also that the situation is similar for the font list in about:preferences: it's a XUL <menulist> element rather than a <select>, but it also builds a XUL scroll frame which is rendered in a popup. So, if we enable APZ in popups, that should start scrolling with APZ as well.

Note that the current pref `apz.popups.enabled` only enables APZ in popups [with remote content](https://searchfox.org/mozilla-central/rev/867cbb1a2b232398616e1aa42f913f37c6cb38e4/widget/nsBaseWidget.cpp#861), which doesn't apply to either <select> or <menulist>. Popups without remote content don't even use OMTC (off-main-thread compositing), which is a prerequisite for APZ.

I discussed this briefly with Jeff. We wouldn't want to blanket-enable OMTC+APZ for all popups, since that would include things like tooltips and OMTC+APZ is a bit heavyweight for a tooltip. However, it may be reasonable to enable them for popups which actually have scrollable content, such as the <select> and <menulist> popups.