As announced, Mozilla has released the first update for Firefox 3.5, prompted by the disclosure of a critical security flaw related to TraceMonkey, the new JavaScript optimizer, earlier this week.

Users who applied the suggested workaround and set javascript.options.jit.content to false via about:config, can reverse it to gain the enhanced performance back. Just double click on the preference to set it to true.

The update also fixes some cases of slow startups due to very long temporary folders scans on Windows.

Oddly, Google Gears, which was finally updated this week is incompatible again. Since there’s no change in extensions API, it’s probably it has a wrong range of compatible versions.

You should be prompted for the update soon, or you can do it manually clicking on Check for Updates… in the Help menu.