Bookmarks and tab URLs don’t contain porn, generally? References are not typically considered explicit, though certainly their language isn’t clear enough about that.

If you bookmark a collection of data: / blob: links then that would be the outlier scenario where you shouldn’t use any third-party server-involved bookmark syncing service, as presumably they’ll all either break or ban you once they find you using their bookmark table space for data storage.

Good point about Relay.

It seems like they might be "use[d]...to...[u]pload, download, transmit, display, or grant access to content that includes graphic depictions of sexuality"

Bookmarks and tabs hinge on how you interpret "grant access". Do URLs to publicly available websites grant you access, or does the phrase only apply to cookies, passwords, login-urls, etc.? I'm pretty certain it would apply to login-urls, email-confirmation emails, password-reset emails, etc, but for normal URLs I could see it either way

> Bookmarks and tab URLs don’t contain porn, generally?

Do URL stubs of porn titles count as explicitly sexual? They can get pretty raunchy

Back in the Wild West of geocities days, I seem to recall animated pornographic favicons.

Favicons are not contained within bookmarks under normal circumstances, but I don’t know if Sync syncs those or if the browser fetches them on each endpoint.

I think this is the most damning point: their terms extend to cover the text in URLs, and so by definition all text including titles and URLs — as well as any pages visited, due to tab syncing — would need to be in compliance with policy. If it’s as clearcut as presented here, anyways. Do the other browser profile syncing services have similar language? Is such overreach unique to Mozilla Corporation?

Though, considering how few people are likely to care about the legal exposure risk of continuing to use Firefox Sync, I don’t imagine this will end up being particularly enforceable in practice.

Blob URL is also just a reference to a (local) resource. I guess another valid example would be something like javascript:document.write(<data>)

Do you know any other?

Then you haven't seen my browser