Crash when closing a second window
This is happening for me and I've submitted a bug report, but was given no link to it so I cannot share that here or follow up on the bug report.
Crash diagnostics coming (post length stopped me putting it here)
Process: Vivaldi 
Version: 1.10.867.48 (1.10.867.48)
Code Type: X86-64 (Native)
Parent Process: launchd 
Responsible: Vivaldi 
User ID: 501
Date/Time: 2017-07-23 10:02:45.990 +1000
OS Version: Mac OS X 10.9.5 (13F1911)
Report Version: 11
Anonymous UUID: C4616A43-1C3D-7264-1AE5-FDD63027BD7D
Sleep/Wake UUID: 60DA321D-050B-4EC7-88F7-0AA6ECE986C3
Crashed Thread: 0 CrBrowserMain Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000128
VM Regions Near 0x128:
__TEXT 0000000107d66000-0000000107d67000 [ 4K] r-x/rwx SM=COW /Applications/Vivaldi.app/Contents/MacOS/Vivaldi
Thread 0 Crashed:: CrBrowserMain Dispatch queue: com.apple.main-thread
0 com.vivaldi.Vivaldi.framework 0x00000001087cbb84 0x107ddf000 + 10406788
1 com.vivaldi.Vivaldi.framework 0x000000010bd71c26 0x107ddf000 + 66661414
2 com.vivaldi.Vivaldi.framework 0x000000010bd71e43 0x107ddf000 + 66661955
3 com.apple.AppKit 0x00007fff8af8b2a6 -[NSApplication _handleGestureEvent:] + 718
4 com.apple.AppKit 0x00007fff8af20f34 -[NSApplication sendEvent:] + 325
5 com.vivaldi.Vivaldi.framework 0x00000001093d81d8 0x107ddf000 + 23040472
6 com.vivaldi.Vivaldi.framework 0x000000010983d68a 0x107ddf000 + 27649674
7 com.vivaldi.Vivaldi.framework 0x00000001093d7f9d 0x107ddf000 + 23039901
8 com.apple.AppKit 0x00007fff8ad719f9 -[NSApplication run] + 646
9 com.vivaldi.Vivaldi.framework 0x000000010984d60e 0x107ddf000 + 27715086
10 com.vivaldi.Vivaldi.framework 0x000000010984cc2c 0x107ddf000 + 27712556
11 com.vivaldi.Vivaldi.framework 0x000000010986ad83 0x107ddf000 + 27835779
12 com.vivaldi.Vivaldi.framework 0x00000001093dd655 0x107ddf000 + 23062101
13 com.vivaldi.Vivaldi.framework 0x00000001082ae384 0x107ddf000 + 5043076
14 com.vivaldi.Vivaldi.framework 0x00000001082b0bd2 0x107ddf000 + 5053394
15 com.vivaldi.Vivaldi.framework 0x00000001082aa23c 0x107ddf000 + 5026364
16 com.vivaldi.Vivaldi.framework 0x000000010939186b 0x107ddf000 + 22751339
17 com.vivaldi.Vivaldi.framework 0x000000010aa64ddc 0x107ddf000 + 46685660
18 com.vivaldi.Vivaldi.framework 0x0000000109390c44 0x107ddf000 + 22748228
19 com.vivaldi.Vivaldi.framework 0x0000000107de28f7 ChromeMain + 119
20 com.vivaldi.Vivaldi 0x0000000107d66daa main + 522
21 libdyld.dylib 0x00007fff92b545fd start + 1
Hi. Did you just install Vivaldi for the first time or did this happen after you upgraded? Have you installed any extensions, and was there anything special or unique about the 2nd window that you closed or was it just a blank window? Does this crash replicate consistently on your system?
I can see that you're using the latest stable version of Vivaldi but running 10.9.5 (Mavericks) on your Mac. (a bit old but still supported, according to the Vivaldi web site.)
I'm running the same version of Vivaldi but on OS X 10.11.6 -- I tried launching Vivaldi, opening a 2nd window, normal and private, with and without web content and while loading web content, tried closing those windows with Command-W/closing the tab/closing the window... but couldn't trigger a crash despite my best efforts.
Any additional info that you can share would be very helpful.
but was given no link to it so I cannot share that here or follow up on the bug report.
When you got the email reply (with the VB number) you can reply to that with all extra information and add any attachments.
BTW What was the VB number?