Late 1970s: microcomputers, explosion of BASIC and ASM development
Early 1980s: proliferation of modems, BBS's become big, Compuserve becomes big- people able to read news online and chat in real-time (but not popular like much later). software stores, software pirating, computer clubs, widespread use of Apple II's in schools. Microsoft Flight Simulator released in 1982 is first super-popular 3D simulation software.
Mid-1980s: GUIs- Macintosh 1984 based on ideas from Xerox PARC.
Late 1980s: Graphics had more colors, more resolution, faster processors. So- cooler games. File servers. 1987 GIF format, 1989 GIF format supporting animation, transparency, metadata- not that popularly used though- was a compuserve thing.
Early 1990s: Internet, realistic quality pictures, webpages/browsing, global file servers. Mosaic web browser. Most pages involved horizontal rule dividers that might be rainbow animated GIFs. Bulleted lists. Under construction GIFs were popular. Linux. JPEG format. Netscape. Blink tags.
Mid 1990s: Windows 95 (with Winsock). IE vs Netscape. IE had marquees. VBScript. (Mocha->LiveScript->)JavaScript. Applets. Shockwave. WebCrawler search. Altavista search. OOP pretty solidly how you should program now with C++ having been around for a while and Java slow but write once/run anywhere and OOP. Apache webserver. CGI: can email from webpage.
Late 1990s: ActionScript. Google search. CSS. Extreme programming. Scrum. JSP. Some using ORM via Toplink. Java session vs. entity beans. IIS. Java multithreading. Amazon gets patent for 1-click ordering. AOL instant messenger. PhP.
Early 2000s: ASP. .Net/C#. Hibernate ORM (free). Choosing between different Java container servers.
Mid 2000s: Use CSS not tables. Rails.
Late 2000s: SPA and automatic updating of content in background via Ajax. Mobile apps. Mobile web. Scala. Cloud computing start. VMs. Streaming video mature. Configuration management via Chef/Puppet.
Early 2010s: Cloud computing standard. Container virtualization. Video conferencing is normal- not just big company office thing. Orchestration of VMs more normal.
Mid 2010s: Container Quantum computing starts at a basic level (not important yet).
Note how I can't really thing of anything recently that has to do with new things in webdev.