can I use Selenium IDE 1.0.10 with FF4.0 yet?
This should be regarded as a hack, but is possible to use Selenium 1.0.10 with Firefox 4 by installing the Add-on Compatibility Reporter extension (it allows you to install and run incompatible versions of your extensions).
The Add-on Compatibility Reporter extension can be found here: https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/
The important part: Press Alt to show the Tools menu. After that it's the same as it used to be.
If installed and enabled then Selenium IDE should be present in the Tools menu, however Selenium IDE 1.0.11 has not yet been released and no officially released version of Selenium IDE supports Firefox 4 yet.