1427629 - 'Lazy' tab loading and tab previews interact badly

Status: RESOLVED WORKSFORME

(Firefox :: Tabbed Browser, defect, P3)

Description

[Justin Bailey]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0
Build ID: 20180102110609

Steps to reproduce:

I noticed that the "tab preview" feature and "lazy loading" interact badly. When lazy loading is enabled (via 'browser.sessionstore.restore_tabs_lazily') and tab previews is enabled (via 'browser.ctrlTab.previews'), then the tab previews only show tabs you've clicked on so far (i.e., have caused to load).

What that means is Ctrl-Tab will not let you navigate to all the tabs visible in the tab bar - frustrating and confusing.

Setting lazy loading to 'false' fixes the problem but is clearly just a workaround.

Comment 1

[Justin Bailey]

Build ID: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0 ID:20180102110609

Comment 2

[Emil Pasca [:emilpasca]]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0

I had tested this issue on Windows 10 x64 with latest Firefox Release(57.0.4) and the latest Nightly (59.0a1-20180104220114) and managed to reproduce the issue.
After switching "browser.ctrlTab.previews" to "true" and having about >20 tabs opened, when using "Ctrl-Tab" shortcut, only up to 6 tab previews are displayed.
Setting "browser.sessionstore.restore_tabs_lazily" to 'false' didn't fixed the problem for me, however, I've observed that on Nightly, "List all x tabs" button is displayed and when clicking it a doorhanger above the "Hamburger" menu icon is displayed, listing all the opened tabs.

I'm not sure if this is an issue or it is the intended behavior, I will assign a component to this and hopefully someone with more knowledge will have a look at it.

Comment 3

[Shane Hughes [:aminomancer]]

The number of tabs shown in the panel is not currently affected by the state of the browsers. Maybe it used to work that way, but currently it doesn't matter if the tab is loaded or "pending" (i.e. discarded) - the max is always 7 (was 6 when this was filed, see bug 1651310). Unloaded tabs won't have a preview thumbnail in the panel if they have never been restored during the session, but they will still be selectable. They could have a thumbnail if they were discarded during the session after having been loaded. But for the purposes of session restore, we can generally expect unrestored tabs to show up in the ctrlTab panel with a blank placeholder image rather than a thumbnail.

We could investigate caching thumbnails for "pending" tabs between sessions, so that thumbnails from previous sessions are restored when the tabs are lazy restored. Maybe we're already supposed to be doing that, but something is broken. Though I think that's a separate issue from this bug.