Downgrading is not recommended in ordinary situations. At the current moment with Firefox 10 automatic updates suspended that could be an exception, but if there is an emergency chemspill release as an update you then miss out on that. Advanced users may consider installing multiple versions of firefox, a simpler method would be to install firefox portable 9 as an additional browser to use for the next few days whilst trying to investigate any hangs, and waiting for any revised further upgrade to a newer version of Firefox 10.

• see installing a previous version of firefox
• also keep watching for updated info in latest firefox issues and possibly also /forums/contributors/708122
• firefox hangs
• http://portableapps.com/apps/internet/firefox_portable#legacy
  even if you install portable 3.6 it is a supported working additional firefox browser

edit
In fact firefox 9 portable, may sensibly; not be easily available either, as it is now an unsupported version. (I also sent you a Private Message look at inbox)

Note version 10.0.1 of firefox is expected to be released very soon; probably on Friday 10th Feb. and should be available also as an upgrade from Firefox 9.

This has improved significantly by deleting my places database as recommended in Firefox hangs or is not responding - How to fix .

Opt in for sending data to firefox, the data is anonymous and helps developers looking at such problems. If you also use the about:telemetry option from the add-on https://addons.mozilla.org/en-US/fire.../abouttelemetry/ then you see a graphical representation of that data it may be of use if some knowledgeable person is to assist with the troubleshooting.

I do not have the specialised knowledge, although I may be interested in the results, but will probably not be online much now until next week.

You may also need to consider memory usage & amount of RAM and page file use.

One of the problems Firefox 10.0.1 is addressing is hangs, possibly hangs related to java use, so that upgrade may help.

The data sending option may not be fully and openly documented at the moment but use, I think:

• Firefox Button -> Options -> | Advanced | -> | General | system defaults
• see options window - advanced panel

If you make a habit of deleting and therefore rebuilding the places.sqlite database at least take the precaution of manually backing up your bookmarks before doing that

• see backing up and restoring bookmarks
• you may also be interested in what is firefox sync, but take care with that, there may have been some recent teething troubles with a change,and it is intended to copy & synchronise NOT be a foolproof backup system