Essential add-on for everyone who does a lot of research. Rated 5 out of 5 stars
I was heartbroken when this stopped working in Firefox 3.6 or 4 (don't remember). As the previous reviewer said, it's now just a matter of updating the max version in the install.rdf file. I have uploaded a new version here: https://dl.dropbox.com/u/371872/find_in_tabs-0.4.0.7-fx-unofficial.xpi
This is identical with 0.4.0.6 except the max number is set to 20.*.*
If you don't trust xpi files from a stranger ;) here's how to do it yourself:
1) Unzip the .xpi file with a file compression software. Don't know how? Just rename the extension to .zip and click on it.
2) Open install.rdf in a text editor (like Notepad). If you don't know how to do it, change the extension .xpi to .txt and double-click on the renamed file.
3) Go to the line that says "<em:maxVersion>3.5.*</em:maxVersion>" and change it to a higher version as needed (my version is <em:maxVersion>20.*.*</em:maxVersion>, but of course it must at least be the version you're currently using). Close and don't forget to save. If you renamed the file to install.txt, change it back to install.rdf.
4) Re-zip all unzipped files and save as .xpi (or rename from .zip to .xpi after saving, if you changed the extension).
5) In Add-ons manager, click on the "cogwheel" icon next to the search field and select "install from file".
I wonder why Mozilla continues to treat this wonderful add-on as "dead." To anyone who can, feel free to upload my unofficial update to addons.mozilla.org.