I think I've seen this for longer than yesterday, however setting high prio in case it's really a regression.

Could be older. I noticed it yesterday, but may have overlooked it earlier.

I am unable to reproduce using Firefox 21, on mw.org, en.wp and my own test wiki.

I occurs for me on different Linux computers, with both FF 21 and FF 22, on all Wikimedia sites (whether logged in or logged out).

Still happens? Because it still doesn't happen for me :)

Yes. On my current setup, with with FF24, it looks like it's not as dramatic as before. The search icon is lower than it should be at the default zoom level, but it only extends past the bottom of the search box if I shrink the zoom level to 90% or lower.

On Chromium, it is aligned properly at all zoom levels.

Gah. Can you test https://gerrit.wikimedia.org/r/#/c/82100/ for me and see if it solves the issue by chance? It's a larger patch to redo the search box on Vector.

(I temporarily deployed it on http://users.v-lo.krakow.pl/~matmarex/testwiki/ , you can test there if you don't have a local wiki to try on.)

The bug is not present on your test wiki. :)

Change 82100 had a related patch set uploaded by Bartosz Dziewoński:
Rewrite rendering of Vector simple search

https://gerrit.wikimedia.org/r/82100

Change 82100 merged by jenkins-bot:
Rewrite rendering of Vector simple search

https://gerrit.wikimedia.org/r/82100