I think Internet Explorer was originally also derived from Netscape - correct?
No. It was a rework of Spyglass Mosaic. Having said that, in a highly competitive arena the Browser War between Netscape and Microsoft ensured that whatever appeared in one would very soon be seen in the other. Due to Netscape's efforts, M$ was playing catch-up until 1997 when (at last) M$ actually listened to its users and produced IE4. At the same time, Netscape decided (apparently) that Microsoft's ways with customers were better, resulting in Netscape Navigator and Netscape Communicator, the latter having an email component.
Unfortunately for Netscape, IE4 was smaller, faster, key-board friendly, had "toys" and client-side support for ICRA .rat files used for family web censorship. It has been mentioned as Microsoft's "best ever" browser, followed by IE5. Netscape never recovered, not least because its ICRA support was served from Netscape, giving users much less granularity and reliability.
By 1997, Mosaic itself was obsolete.
In 1998, M$ merged the display part of IE with the W98 OS, thus cementing their monopoly on browsers. This incorporation with the OS ensured that IE would always load faster than any other browser, until K-Meleon.
Gigabyte H61M-USB3-B3 r2.0, I5-2400 3.10GHz, 4GB RAM; W7HPx64 SP1, Lotus SmartSuite 9.8, K-Meleon 76RC, Pale Moon 26.4.1, IE11, Clyton email 15.0, Foxit Reader 18.104.22.1686, PaintShop Pro 6.02, ZAM Free 2.74, SuRun 22.214.171.124, VoodooShield 3.59b
"Learning is not compulsory. Neither is survival." Dr. W. Edwards Deming.