FYI: I filed #20528 about the missing PDFs from the webarchive. The webarchive should be reliable, and if it is not, there may be some bigger problems that may necessitate an alternative archive for PDF files.

Trivial and it helps to fix some tests issues in the Firefox ci.

Yes, for now merging this is fine but that the file disappears is a bigger issue (and in general why we do our best to avoid linked test cases and prefer in-repo test cases where possible).

Moreover, while this works for Talos it'll still break if someone does a clean clone of PDF.js and then attempts to download the PDFs.

I managed to find the original paper at https://dl.acm.org/doi/pdf/10.1145/1120725.1120923, but it's not the same PDF because it has an extra page, so the question is: does that file still cover the original bug, or was it re-generated to no longer have the issue?