MLZ: Delay on drag and drop to a collection

I'm experiencing a significant delay on dragging and dropping items into collections: it takes about five seconds for the cursor to change from an arrow to an item-and-plus-sign, and during that time Firefox has high CPU usage (up to about 40%).

Some details:
- latest Multilingual Zotero (4.0.21m474)
- latest Firefox (33.02) in Windows 8.1 Pro Update 1, 64-bit
- reproduced with all other Firefox extensions disabled
- category tag is hidden
- library is under 1000 items
- the delay happens whatever the number of items being operated on

I've created a log file of the operation (dragging and dropping a single item with no attached file from Unfiled Items to a collection): D35405998.

Any suggestions?
  • edited October 29, 2014
    I can't view the debug output, but I'll take a look this weekend. I have a rough idea of what the problem might be (it may be instantiating the export citation style as part of the drag operation, which shouldn't be necessary when dragging to a collection).

    If you don't hear back by the end of the weekend, feel free to ping this thread.
  • A drag operation was instantiating the CSL processor (a relatively heavy operation) twice each time. I've adjusted the code a little to do it only once, which will speed things up a little.

    Zotero works the same way, but the lag is not so noticeable because most of the repository styles are much smaller than the MLZ versions. It's still unnecessary overhead, though, so I have proposed the change for official Zotero as well.

    I have a potentially much better solution in mind, but that will take some time to plan and code.
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