Did you copy the entire C:\Documents and Settings\user-name\Application Data\Mozilla\Firefox\ folder from the old drive? If not, can you? If so, make a copy and save that folder just-in-case.

If so, you could replace that folder on the new installation with the \Profiles\ folder [with your Profiles inside of it] and the profiles.ini file [deleting any other files / folders that may also be in the "Firefox" folder] - then replace with the same named folder from the old failed drive. Note that you'll lose anything that you have already done with the new installation / Profile! Your Profile folder contains all your personal data and customizations, including search plugins, themes, extensions and their data / customizations - but not plugins. But if the Logon User Name is different on the new installation than the old one, any extension that used an absolute file path in its prefs will have problems. Easily rectified though, by editing the file path in the prefs,js file - keeping the line brake formatting intact. Extensions created after the era of Firefox 2.0 or 3.0, due to changes in the "rules" for creating extensions usually aren't an issue, but some real old extensions that have only needed minor "tweaks" since that era may still be using absolute paths - although I haven't seen that myself since Firefox Firefox 3.6 or 4.0.

Notice instead of "Add-ons" I mentioned the 4 types of "Add-ons" separately - Plugins are considered "Add-ons" but they are not installed in the Profile [except for those incorrectly labeled as a "plugin", when they are installed via an XPI file], but rather into the operating system where Firefox "finds" them via the Registry.

Note: Migration articles may tell you not to re-use the prefs.js file, due to an issue that I feel is easily fixed with a little bit of inspection and editing. I think you can handle that - my perception is that you have a small shovel in your toolbox, that should you run into a problem you are capable of doing a little bit of digging and fixing minor issues with files paths - once you are forewarned.

Overall, if you are going Firefox 35 to 35 or even Firefox 34 to 35, I don't think you are going to run into any issues that you can't handle [as I cross my fingers and "hope" I am not overlooking anything obvious].

As far as recovering "data" for individual extensions - there are many ways that extension developers have used to store their data and prefs. The original way was to save it in prefs.js or their own .rdf file in the Profile folder. Then as Firefox was developed more, developers started using their own folders in the Profile folder. And since Mozilla started using sqlite database files back in Firefox 3.0, Mozilla has been expanding their own use of sqlite, as have extension developers. Stylish uses the stylish.sqlite file for storing "styles data", but something in the back of my mine says to me that the "index" may not be in that file with the data. But then again, I may be confusing myself with an issue I had with GreaseMonkey awhile back when I copied the gm_scripts folder into a new Profile and with GreaseMonkey already installed but with no scripts. Those GM scripts did work, but I couldn't see them or edit them - they didn't appear in the GM extension UI window in Firefox.

Thank you! Recovering the Stylish css data was successful, which was the main thing I was after. Copying over the stylish.sqlite file into the new profile folder did the trick.

Also, I had FF31 on the HDD that crashed, and when I migrated my profile data also copied over the prefs.js file. I figured that, since it was a new install, I had nothing to lose by trying it. All path pointers have been working so far.

Anyway, thanks again!