With the Firefox 3.5b4 release, we’ve enabled the 3.5.* maxver in the AMO Developer tools. For the vast majority of add-ons without binary components, you can simply update your maxver to 3.5.* and it will be compatible with all versions of Firefox 3.5 through the release. If you do have a binary component, you should only have to recompile your code against the latest- for more info see the Firefox wiki.