So here is simple and effective hack for this problem…
First and only once you have to understand how the compatibility is written in the code of add-on….And it is very simple to understand.
1. First get the add-on file like add-on-name.xpi
2. Rename to add-on-name.zip
3. Open it with zip
4. Look for install.rdf
5. Open it with WordPad.
(In case if it is not open in WordPad, extract it and then open it with WordPad)
6. Now you will notice that:(Sometimes this differ but the following red lines must occur)
<!-- Target Application this extension can install into,
with minimum and maximum supported versions. -->
<!-- Front End MetaData -->
<em:description>A sample extension.</em:description>
<em:creator>Addon Author Name</em:creator>
here is the hack,
These two lines defines that,
Minimum compatibility version is 1.5
Maximum compatibility version is 2.5.
8. Now in order to make it compatible, we have to just change these two parameters.
e.g. If I want to make add-on like above to compatible with version 3.0.0 to 3.5.3 then replace above lines with following
9. Now save the install.rdf.
10. Again rename it to add-on-name.xpi
Now, your incompatible add-on is get compatible with your choice of Firefox version.
NOTE: The percentage of success of this hack is 99.99%. This is because some add-on gets compatible with updates of Firefox versions but not working fully.
You may put your comments over here, so others get trust on this. And if you not getting this hack, you may tell here, I will make it compatible for you and send to you...But I want that you people try this yourself, its so simple, else I am here for you...