Why file URLs dont work on Mozilla/Firefox/etc. At work we were using DemoShield in a Windows installation,which I thought was dumb since we were using this heavy program for something that could easily be done with simple HTML. So when we did a seperate installation for Linux, I suggested that we just use HTML. Seemed like a good idea, but we kept getting strange behavior - the page wouldn't load, etc. I recently started using Firefox as my browser (the boys back in Redmond would be appalled - I used to nominally be part of the IE team - my name was even in the "easter Egg credits for IE 4) and I noticed that I couldn’t do things like open the “About-DecisionSpace.html” file from the filers. Very strange I thought. So I did some looking. Turns out Mozilla (which Firefox is based on) considers those a security issue, and won’t open them: Bugzilla 122022 Bugzilla 84128 So I did a test with the ‘javascript console’ up and saw this: Security Error: Content at http://bugzilla.mozilla.org/show_bug.cgi?id=122022 may not load or link to file://///afiler1/dsbuilds/DecisionSpace/branch_2003-15-L-9/win32/daily/40903.02/About-DecisionSpace.html. The 1st bug link above does list a workaround: Also, I read in Bug 66194 that the way for individual users to fix this problem is to set the pref called "security.checkloaduri" to "false". This is handy for getting around this problem (but exposing yourself to the security hole). or this suggestion for wording when this happens: "Security violation: links to local files currently disabled. To enable this feature, you can set the variable security.checkloadURI in your prefs.js. But be aware that you open a possible security hole, esp. in connection with javascript!" So that explains why we were having difficulties with things like the ‘demoshield html’ on Linux. There are also many duplicates of this bug. Aha – If I close all instances of the browser completely, then double clicking on About-DecisionSpace.html from explorer works. Strange, because when I got the error it was trying to load the About… in a different browser window than the one I had open. P.S. on firefox, the preferences file is actually at C:\Program Files\Mozilla Firefox\greprefs\all.js