Create new folder instead of SplitTab

[Lonmine]

I just migrated to zen and i am loving it so far, but the thing that i miss the most is the ability to create tab groups just by dropping tabs on top of each other, on zen this is currently SplitTabs, and i noticed that when you drop a tab on top of the active web page it already makes a SplitTab so if i could have the option i would appreciate.

[jmbarrancoml]

+1 to this, and I'd like to build it if you're open to it.

The first time I dragged a tab on top of another one in the sidebar I expected a folder. That's what the iOS home screen and Arc do. Zen gives me a split view instead, so grouping two loose tabs means going through "New folder" in the context menu or dragging into a folder I created before. Firefox does the folder thing upstream with tab groups too, Zen has that path switched off.

I had a look at how split-on-drop works in ZenDragAndDrop.js. The hold-over-tab gesture has a delay, a hit zone and a preview, so a folder could reuse all of that. My idea is a pref, something like zen.folders.create-on-drop, off by default:

• off: the gesture keeps creating a split view, nothing changes for anyone
• on: hovering a tab over another tab for the same delay shows a folder preview, and dropping calls gZenFolders.createFolder([target, dragged]) in place with the rename box open, same as "New folder" does today

Scope-wise it's the two drag handlers in ZenDragAndDrop.js, a bit of CSS for the preview and a browser test. No new settings UI unless you want a toggle later. It can't be a mod since mods are CSS only.

If this works for you I'll open the PR against dev.