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Had exactly the same problem and found the following workaround:

1. Paste the exported string into a text editor

2. Find the first occurrence of the word "function". There will be several of them one after another looking like this: "key": function key() { [native code] },"getItem": function getItem() { [native code] }, etc.

3. Remove all of them - they don't look like valid JSON parts (and also do not pass JSON validators that you can easily find online)

4. After the invalid JSON part is removed, second attempt to import the string will also fail due to another problem: immediately before 1st invalid entry (with "function" word which you removed), there is the entry '"length": 43' (in your case 43 can be different number probably). While it is valid JSON entry, it cannot be imported because "length" is RO property. So remove this entry also.

After those 2 corrections, my string was imported successfully. I don't know what those settings mean but I didn't mention any problems after restoring Sidewise settings on 2nd PC (except those reported here by other people and not related to export/import) 

"waking up a hibernated tab doesn't place it back to its original location but instead creates a new tab" - same in Windows machine, probably related to chrome and/or Sidewise update, as mentioned in another recent report here