Cross-browser compatibility remains a significant engineering challenge for developers of jQuery-based mobile web applications, despite the library’s original mandate to normalize DOM and event inconsistencies across browsers. Modern mobile ecosystems have reintroduced fragmentation through divergent rendering engines, inconsistent levels of HTML5 and CSS3 implementation, vendor specific optimizations, and OEM modified Android browsers. These differences manifest in subtle yet severe failure modes including inconsistencies in touch event handling, viewport calculation, hardware-accelerated animation behavior, and CSS layout interpretation which jQuery alone cannot reliably abstract. This article provides a systematic analysis of compatibility breakdowns observed in real-world jQuery driven mobile interfaces, with emphasis on event timing anomalies, animation performance cliffs, and plugin instability across Chromium, WebKit, and Gecko based mobile browsers. Through targeted case studies and empirical testing, I identify recurring technical patterns and evaluate the limits of jQuery’s abstraction layer in a post-desktop web context. This paper further discusses resilience strategies such as progressive enhancement, feature-based capability detection, conditional polyfilling, and selective delegation to modern touch and animation libraries. The paper concludes by outlining best practices and architectural guidance for developers seeking to build forward compatible, high-performance mobile experiences on aging jQuery stacks while acknowledging the technology’s diminishing suitability in the era of evergreen browsers, PWAs, and framework-native touch models.