In terms of measuring performance impact of this fix: 1. Telemetry Looking at the [query](https://sql.telemetry.mozilla.org/queries/113437/source?p_build_date_after=2026-01-02&p_channel=nightly&p_days=30&p_group_by=submission_date&p_minimum_entries_group=0#278149) in which we plot the performance metrics by submission date, splitting the data into builds with the fix (Jan 3 and later) versus builds without the fix there is some indication that we are seeing an improvement. **However,** there is a huge sampling bias here because we are also looking at the ~60% of Fenix nightly users who upgraded to the latest vs the 40% who didn't. So while promising, I think this is low-confidence data (although observing impact on Beta and Release will be helpful.) 2. Automated performance suites Unfortunately I cannot do an automated sweep of top sites to measure impact because our performance test harness, browsertime, disables tracking protection and safeBrowsing features and so the issue is hidden in that environment. I just logged this in bug 2008355 3. Manual examination of top mobile sites I performed a manual scan of select top-50 mobile sites and I did find some examples of significant improvements from this fix. On https://www.target.com/, what is effectively the [hero asset](https://target.scene7.com/is/image/Target/GUEST_ba50811b-7038-4b3b-80fe-06c7e31b3248?wid=526&qlt=80&fmt=pjpeg) is tailed and the request takes about 1.4 seconds to complete. [profile](https://share.firefox.dev/3L3Z4vh) Compare to a profile with the fix applied in which the request is made in ~340ms. [profile](https://share.firefox.dev/3YpUsTd). Spotify.com is another example as key assets are retrieved from google storage and thus tailed. Here the [background image](https://storage.googleapis.com/pr-newsroom-wp/1/2026/01/FTR-1440x820-14745983475934-1440x820.jpg) is delayed for over 2.5 seconds. [Profile](https://share.firefox.dev/3Ny4bV3)
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In terms of measuring performance impact of this fix: 1. Telemetry Looking at the [query](https://sql.telemetry.mozilla.org/queries/113437/source?p_build_date_after=2026-01-02&p_channel=nightly&p_days=30&p_group_by=submission_date&p_minimum_entries_group=0#278149) in which we plot the performance metrics by submission date, splitting the data into builds _before_ the fix and builds _after_ the fix (jan 2, 2026) there is some indication of an improvement. **However,** there is a huge sampling bias here because we are also looking at the ~60% of Fenix nightly users who upgraded to the latest vs the 40% who didn't. So while promising, I think this is low-confidence data (although observing impact on Beta and Release will be helpful.) 2. Automated performance suites Unfortunately I cannot do an automated sweep of top sites to measure impact because our performance test harness, browsertime, disables tracking protection and safeBrowsing features and so the issue is hidden in that environment. I just logged this in bug 2008355 3. Manual examination of top mobile sites I performed a manual scan of select top-50 mobile sites and I did find some examples of significant improvements from this fix. On https://www.target.com/, what is effectively the [hero asset](https://target.scene7.com/is/image/Target/GUEST_ba50811b-7038-4b3b-80fe-06c7e31b3248?wid=526&qlt=80&fmt=pjpeg) is tailed and the request takes about 1.4 seconds to complete. [profile](https://share.firefox.dev/3L3Z4vh) Compare to a profile with the fix applied in which the request is made in ~340ms. [profile](https://share.firefox.dev/3YpUsTd). Spotify.com is another example as key assets are retrieved from google storage and thus tailed. Here the [background image](https://storage.googleapis.com/pr-newsroom-wp/1/2026/01/FTR-1440x820-14745983475934-1440x820.jpg) is delayed for over 2.5 seconds. [Profile](https://share.firefox.dev/3Ny4bV3)