XUL attribute persistence is handled by the XUL document, so when we move to HTML the same behavior does not exist. Example test that is broken: browser/base/content/test/performance/browser_window_resize.js

Previously, XUL attribute persistence was mainly handled by the XUL document which doesn't work for browser.xhtml. Move the attribute watching and persisting code to the XUL element and move the loading and setting of the persisted attributes into XULStore, so they can be used by XUL and HTML. How the stored values are applied on document load is handled slightly differently in XUL and HTML. In a XUL document, the attributes are automatically applied after parse. In an HTML document we don't want to have this behavior by default, so applyPersistentAttributes must be called explicitly if the page wants to use this feature. This also gives the page finer control over when to apply the persisted attributes.

Comment on attachment 9011856 [details] Bug 1490464 - Fix XUL attribute persistence for browser.xhtml. r=smaug Olli Pettay [:smaug] (r- if the bug doesn't explain what the change(s) are about.) has approved the revision.

Comment on attachment 9011856 [details] Bug 1490464 - Fix XUL attribute persistence for browser.xhtml. r=smaug Olli Pettay [:smaug] (r- if the bug doesn't explain what the change(s) are about.) has requested changes to the revision.

Pushed by bdahl@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/4350340785e4 Fix XUL attribute persistence for browser.xhtml. r=smaug