I’d noticed it as 2.58 in Firefox’s dev tools, so when you say 2.54, I’m curious. #ab9ea2 on #ffffff. https://webaim.org/resources/contrastchecker/ says 2.57, https://contrast-ratio.org/#%23ab9ea2-on-white says 2.57 and on hover expands that to 2.5785676343306743. I presume Firefox is rounding, while the other two are truncating. Truncating actually feels more useful for how people are too likely to use such things—taking values as low as they can while still complying.

The new, superior method is https://www.myndex.com/APCA/. It yields an Lc of 50.4, which is (as you’d expect) wildly unsuitable for body text.