NiftySplit (Port) per THFYM

Chrome's classic "NiftySplit" is now ported to that one other browser.

All credit goes to the extension's original author, Arno van den Brink. Seriously, this wouldn't be possible without him; I wrote very little actual code, and just tweaked a few things for Firefox compatibility. I can really take no credit for this.

From the Chrome store (and the original author):

Use NiftySplit to split [your browser] into two windows. Any link you click in the left window will load in the right window.

Is this useful? Yes!

You can now browse your favorite website and visit links without losing the main page. No need to use the Back button or open-and-close tabs all the time. This makes browsing websites like Reddit or Wikipedia a thing of pure joy.

Give it a try and let me know what you think!

*** now with multi-monitor support! ***

New in v0.8:
- Multi-Monitor support!
- Removed 'tabs' and 'storage' permissions
- Fixed bug where options were not being saved
- Added 'reset options to default' button
- Set default action for main window maximize to: maximize child, do not end session
- Some bug fixes

New in v0.7:
- Shift-click to open links in the left-hand window
- Window position can be customized and stored
- Support for taskbar-on-the-left layout
- Support for Incognito windows

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Added by THFYM:

New in v0.8.2:
- Cleaned up a few things to list the extension on Firefox's Add-On Store

New in v0.8.1:
- Added support for Mozilla Firefox