Bluesky serves two types of sample versions: feed_thumbnail and feed_fullsize. These are not the best public versions on the site. In order to access higher-quality versions, you need to reformat the URL to retrieve the original blob instead. Additionally, Bluesky uses a format for accounts and posts that breaks when usernames are changed. Solving these issues requires changing the URL to include the user's DID (decentralized identifier), but performing this process manually is tedious.
The two userscripts below will automatically get the best image quality and resolve to more stable links to Bluesky account and post pages:
Bluesky higher-quality image redirect: https://gist.github.com/Tarrgon/a58375cd3c1f15d8fd4238a2a7df35b5
Bluesky stable links redirect: https://gist.github.com/Tarrgon/c84f267a4f97314090b4870760b8fb8f
In order to use these, you will need a userscript manager. An example of a userscript manager is Tampermonkey: https://www.tampermonkey.net/
Once you install a userscript manager extension of your choice, copy-paste the scripts linked above into new scripts and save. Bluesky image links will now reload to higher-quality versions, and post and account links will be more stable for archiving purposes. The image quality improvement will vary from almost imperceptible to significantly less JPEG compression, but this version will always be superior.
Wayback Machine links to the above scripts in the event that the GitHub pages are unavailable in the future (these may be out of date):
https://web.archive.org/web/20250427005625/https://gist.github.com/Tarrgon/a58375cd3c1f15d8fd4238a2a7df35b5
https://web.archive.org/web/20250509034554/https://gist.github.com/Tarrgon/c84f267a4f97314090b4870760b8fb8f
Updated