Third party advertising and tracking (A&T) are pervasive across the web, yet user exposure varies significantly with browser choice, browsing location, and hosting jurisdiction. We systematically study how these three factors shape tracking by conducting synchronized crawls of 743 popular websites from 8 geographic vantage points using 4 browsers and 2 consent states. Our analysis reveals that browser choice, user location, and hosting jurisdiction each shape tracking exposure in distinct ways. Privacy focused browsers block more third party trackers, reducing observed A&T domains by up to 30% in permissive regulatory environments, but offer smaller relative gains in stricter regions. User location influences the tracking volume, the prevalence of consent banners, and the extent of cross border tracking: GDPR regulated locations exhibit about 80% fewer third party A&T domains before consent and keep 89-91% of A&T requests within the EEA or adequacy countries. Hosting jurisdiction plays a smaller role; tracking exposure varies most strongly with inferred user location rather than where sites are hosted. These findings underscore both the power and limitations of user agency, informing the design of privacy tools, regulatory enforcement strategies, and future measurement methodologies.

翻译：第三方广告与追踪（A&T）在网络中无处不在，但用户接触程度因浏览器选择、浏览位置和托管司法管辖区的不同而存在显著差异。我们通过使用4种浏览器和2种同意状态，从8个地理观测点对743个热门网站进行同步爬取，系统研究了这三个因素如何影响追踪行为。分析表明，浏览器选择、用户位置和托管司法管辖区各自以不同方式塑造了追踪暴露程度。注重隐私的浏览器能拦截更多第三方追踪器，在宽松监管环境下可减少多达30%的观测到A&T域名，但在严格监管地区的相对收益较小。用户位置影响追踪量、同意横幅的普遍性以及跨境追踪的程度：受GDPR监管的位置在同意前显示的第三方A&T域名减少约80%，并将89-91%的A&T请求限制在EEA或充分性认定国家范围内。托管司法管辖区的作用较小；追踪暴露程度主要随推断的用户位置而非网站托管地点而变化。这些发现既凸显了用户自主权的力量，也揭示了其局限性，为隐私工具设计、监管执法策略和未来测量方法提供了参考。