Firefox(20.0.1) is ignoring my proxy server for google searches from website and the search box. It works for all other search engines and chrome/safari.

Question

firefox(20.0.1)
squid (port 3128) and dansguardian (port 8080) not running in transparent mode.
I am applying blacklists and a custom url regex to apply "safe=vss", this works for all browsers and all search engines except firefox using google search engine.
Search engines tested (bing, yahoo, norton, ask, amazon, avg, ebay) - all work.
Links from the search results are blocked by content filter, but search results still appear and google images are still shown. This does not happen in Chrome(23.0.1271.97), IE9(9.0.8), Opera(12.14) or Safari(5.1.7) with the same settings.
No log entry appears in Dansguardian access.log implying proxy settings are being ignored for just this combination.

Answer 1

I can't think of a reason that one particular webpage would behave differently from all the others, i.e., if you are starting at google.com and running a search using the form in the page, I'm not aware of any reason for Firefox to handle that specially just because it's Google.
Does it make a difference if you disable JavaScript when using Google? If that yields the results you expect, perhaps Google's XMLHttpRequest AJAX traffic is bypassing your filters?
The search bar has its own code, so someone would need to look at that to see whether/why it bypasses your proxy if the above hypothesis does not apply.