One thing I noticed about both the REI and MountainHardwear sites is that they display ads from the DoubleClick network. I wonder whether there is a bad ad going around that only rotates in now and then? Could someone test with and without an ad blocker?
Happening on many sites, including Classmates.com (Memory Lane). Checked source code and there is no DoubleClick ad on there. (Also blocked by my Hosts file).
It's possible that one of your add-ons isn't fully compatible with Firefox 12. Could you try Firefox's Safe Mode to see whether we can rule that out?
First, I recommend backing up your Firefox settings in case something goes wrong. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)
Next, restart Firefox in Safe Mode using
Help > Restart with Add-ons Disabled
In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode."
If the problem sites loads normally, this points to an add-on or custom setting as the likely problem.
Any new info?
Do you have to be logged in to the site to see the problem?
No, and it does not happen on a laptop running FF 11, or on IE 8. Both computers are running Win XP SP3, latest Java, latest FlashPlayer, etc. Only difference is FF version....
Tried disabling all plug-ins, no luck. I have "IE Tab 2" which causes the affected page to render correctly. Found earlier version of FF (11.0) but it's just a list of files, and I have no idea how to install it, without screwing up my entire system and all bookmarks, etc etc.
More and more websites are affected. Here's another, very public, one: http://www.landsend.com/