Rather than try and force Firefox to deal with thousands of tabs, it might be easier to use an add-on like SingleFile to download the tabs as self-contained HTML files. Then once you have the pages downloaded you can search their contents using free tools like Agent Ransack or DocFetcher.
If you still want to keep the data in your browser, then how about using a service like Instapaper that lets you save pages you want to read/reference later?
Rather than try and force Firefox to deal with thousands of tabs, it might be easier to use an add-on like SingleFile to download the tabs as self-contained HTML files. Then once you have the pages downloaded you can search their contents using free tools like Agent Ransack or DocFetcher.
If you still want to keep the data in your browser, then how about using a service like Instapaper that lets you save pages you want to read/reference later?