The claim by tinus_hn is that FrontPage - Microsoft's HTML editing tool - created pages that crash Netscape.
While it would arguably be Netscape's fault if Netscape actually crashes (rather than simply failing to display a malformed input) at that time in the browser wars there were plenty of energy going into creating incompatible new 'features' - such as Microsoft's own JavaScript competitor, VBScript [1], vector imaging format (AutoShapes) and animation tags (DHTML)
And Microsoft did intentionally sabotage competitors products in the 1990s with approval from the highest levels of the business - such as DR-DOS [2].
So while I'm not aware of any claims Microsoft sabotaged the OS to make Netscape crash, they'd sabotaged the OS to make other competing products crash, and they certainly added a lot of 'features' so web pages wouldn't render right on Netscape.
[1] http://www.gbengasesan.com/fyp/43/ch5.htm
[2] https://en.wikipedia.org/wiki/AARD_code