Add Firefox Sync support for workspaces, folders, and pinned tabs

[bdbch]

This adds a new Firefox Sync engine that syncs:

• Workspaces (name, icon, theme, container associations)
• Pinned tabs and essential tabs (URLs, custom labels, positions)
• Folders with full nesting support and custom icons

The sync is enabled by default when Firefox Sync is active. It uses a single-record approach similar to the Prefs engine, with last-writer-wins conflict resolution.

Key things:

• Tabs sync as lazy (don't load until clicked)
• Custom tab labels are preserved
• Folder icons sync correctly
• Interleaved ordering of tabs/folders is maintained
• Essential tabs sync to the essentials container (workspace-independent)
• Safety checks prevent empty/stale data from overwriting good data

The engine triggers sync on workspace changes, folder changes, pinned tab changes, tab moves, and folder icon updates.

[A2va]

Does it also sync the containers linked to a workspace ?

[bdbch]

Does it also sync the containers linked to a workspace ?

Not sure, would have to double verify. Right now I'm stuck with stabilizing the sync. It's not ready yet for use but from my last test I'm sure the container ID at least is synced. The more interesting question would be how to make sure specific containers are belonging to each other cross device.

[TheReyzer]

I hope it came soon. just waiting this for change from Arc Browser.

[bdbch]

I will try to get some time to work on this. Last week was very busy. Since this is my first time working on Firefox & Sync Engines directly I want to make sure this 100% works.

With my last changes I made I was able to get tabs synced but workspace changes very often were delayed or overwritten by different clients.

I will work on this today or tomorrow and try to find a solution that is stable.

[TheReyzer]

I will try to get some time to work on this. Last week was very busy. Since this is my first time working on Firefox & Sync Engines directly I want to make sure this 100% works.

With my last changes I made I was able to get tabs synced but workspace changes very often were delayed or overwritten by different clients.

I will work on this today or tomorrow and try to find a solution that is stable.

Hope you get it!

[mr-cheffy]

@bdbch is this ready for review? Have my concerns I said before been fixed? No pressure