April patch set for TenFourFox

As promised, there are new changesets to pick up in the TenFourFox tree. (If you're new to rolling your own TenFourFox build, these instructions still generally apply.) I've tried to limit their scope so that people with a partial build can just pull the changes (git pull) and gmake -f client.mk build without having to "clobber" the tree (completely erase and start over). You'll have to do that for the new ESR when that comes out in a couple months, but I'll spare you that today. Most of these patches are security-related, including one that prevents naughty cookies which would affect us as well, though the rest are mostly crash-preventers and would require PowerPC-specific attacks to be exploitable. There is also an update to the ATSUI font blacklist. As always, if you find problematic fonts that need to be suppressed, post them to issue 566 or in the comments, but read this first.

However, there is one feature update in this patchset: a CSS grid whitelist. Firefox 45, which is the heavily patched underpinning of TenFourFox FPR, has a partially working implementation of CSS grid as explained in this MDN article. CSS grid layout is a more flexible and more generalized way of putting elements on a page than the earlier tables method. Go ahead and try to read that article with the current build before you pull the changes and you'll notice that the page has weirdly scrunched up elements (before a script runs and blanks the whole page with an error). After you build with the updates, you'll notice that while the page still doesn't lay out perfectly right, you can now actually read things. That's because there's a whitelist entry now in TenFourFox that allows grid automatically on developer.mozilla.org (a new layout.css.grid.host.developer.mozilla.org preference defaults to true which is checked for by new code in the CSS parser, and there is also an entry in the problematic scripts filter to block the script that ends up blanking the page when it bugs out). The other issues on that page are unrelated to CSS grid.

This will change things for people who set the global pref layout.css.grid.enabled to true, which we have never shipped in TenFourFox because of (at times significant) bugs in the implementation. This pref is now true, but unless the URL hostname is in the whitelist, CSS grid will still be disabled dynamically and is never enabled for chrome resources. If you set the global pref to false, however, then CSS grid is disabled everywhere. If you were using this for a particular site that lays out better with grid on, post the URL to issue 659 or in the comments and I'll consider adding it to the default set (or add it yourself in about:config).

The next ESR (Firefox 115) comes out end of June-early July, and we'll do the usual root updates then.