Yes, I agree that the situation has gotten somewhat better. However, the OperaView problem is driving me nuts. I downloaded Mr. Tech Toolkit after seeing you and other mention it, but I wasn't able to figure out how I might use it to get the OperaView extension to work again. I'd love to know.
This is not a guaranteed fix. It'll only disable the version check that Firefox does when it checks to see if an extension will work with the browser. If there are inherent compatibilities with the extension this is not going to help you. Open up the options in MR Tech Toolkit. Click on the Miscellaneous toolbar button and then on the XPI Install Options tab. The first checkbox is what you are looking for: Enable Addons Compatibility Checking. By default it is checked. Uncheck it and when you go to install OperaView or any other extension Firefox will not balk if the versions don't match up.
Beware this is a browser-wide setting so no addons will be compatibility checked so I prefer this second way to get things work & it restricts the compatibility check disable to the extension you are trying to get to work. First you would download the extension and save it to the folder of your choice. Then you would open the XPI file with your favorite archiver whether it be PowerArchiver, Winzip, WinRAR, or whatever so long as it can open zip files as that's all an XPI file is.
Once you've done that in the root directory of the archive you are going to find a file called install.rdf. Extract that file and open it in your favorite text editor. Do a search for maxversion and your search will turn up something similar to this:
You would just need to change that line to read as so:
Save install.rdf with your changes. If you still have the archive open in your archiver just drag and drop your new install.rdf on the open archive window & your archiver should ask you if you want to replace the old file with your new one. Just say yes. Close the archive & then drag th XPI & drop it on your open Firefox window & the install addon procedure will commence. The only difference is this time Firefox will see that the XPI is compatible with all v3.x versions of Firefox & will let you install it.
If all goes well there won't be any real incompatibilities and your extension will work. If it does, tuck your diva-made XPI away somewhere safe & if you ever should need to reinstall Firefox for whatever reason your custom XPI will be ready to install without having to modify it again.