Can anyone explain how to functionally interact with Mastodon links?

Step 1. I get sent a link to a post on meow.social or mastodon.art

Step 2. I open it in browser

Step 3. I try to boost or like it but can't bc I'm not signed in to meow.social or mastodon.art as I don't have accounts there

FWIW this seems like one of the biggest shortcomings of fediverse atm, it's a huge PITA to boost stuff that I get linked. If smn has to work on a meaningless task for more than 10 seconds they just won't