ecmanaut

When I occasionally need to check how far back a feature was introduced in Firefox, it usually turns out I only have the last few versions installed, and takes a while before I find where mozilla.org hit them, so here goes: a complete archive of the latest (mac -- tweak the urls or browse yourself for Linux, Windows or otherwise) release of every major version of Firefox from 0.8 to date (at current time of writing, 3.6.13 is the most recent Firefox released) off of ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/, where mozilla.org hosts them, and the Firebug releases you need to do any useful web development work with them:

• Firefox 4.0 beta 8 (Gecko 2 / Firebug 1.7X.0a7)
  Note: as neither of is released yet, consider both links outdated when you read this (the Firebug xpi especially is in development, as hinted by the X)
• Firefox 3.6.13 (Gecko 1.9.2 / Firebug 1.6.0 or 1.5.4)
• Firefox 3.5.16 (Gecko 1.9.1 / Firebug 1.5.4)
• Firefox 3.0.19 (Gecko 1.9 / Firebug 1.4.5)
• Firefox 2.0.0.20 (Gecko 1.8.1 / Firebug 1.3.4b2, 1.2.0 or Firebug 1.0.5)
• Firefox 1.5.0.12 (Gecko 1.8 / Firebug 1.05)
• Firefox 1.0.8 (Gecko 1.7)
• Firefox 0.9.3 (Gecko 0.9)
• Firefox 0.8 (Gecko 0.8)

(Corresponding Gecko and Firebug versions, the second and third most messy to find Firefox entity, from the Gecko page on MDC and the install.rdf of the corresponding Firebug xpi:s archived at getfirebug.com.)

Never ever download and install Firefox from any other site! There is a huge, shady "pay per install" market of people bundling other people's software with malware (bot nets, typically); read all about it from Symantec (pdf) or Kevin Stevens (also pdf, the latter from Black Hat DC 2010). This goes for all executable programs you download and install on your machine; if you have no reason to trust the source, get it from a source you do trust.