Rated 5 out of 5 stars
To install this Add-on for FF 3.6.x
(works just fine-I'm using 3.6.6 on Mac OS X 10.4.11):
1. install MR Tech Toolkit.
2. Once installed, go to preferences under "Miscellaneous". Click on the tab for "XPI Install Options" and UNCHECK "Enable Addons Compatibility Checking".
NOTE: This turns off checking for ALL extensions (but you will only do this temporarily--see step 5 below).
There may be other add-ons that can turn this checking off but MR Tech Toolkit is the only one I know. This step is critical to be able to download FIT addon.
3. Now install this add-on from here.
4. Once Find in Tabs is installed, go to the Extensions list, find "Find In Tabs" extension. Right-click and select "Make Compatible" (this only applies to the add-on selected). Now this add-on will be enabled when you restart FF 3.6.x.
5. Now we have to re-enable Add-on Compatibility Checking for the rest of the add-ons. Just reverse the steps in step 2. by re-checking the "Enable Addons Compatibility Checking".