The mypoints and swagbucks along with several other add ons just disappear frequently and I have to reinstall.
I periodically open Firefox and all of my add ons are gone. When I go to swagbucks.com to reinstall the swagbucks toolbar it downloads it and re-installs and then Firefox prompts me to agree to install all of the other missing add ons. The same thing happens if I start at mypoints to reinstall.
If you see disabled, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to check if there is a compatibility update available.
If this hasn't helped then also try to delete the addons.sqlite file.
You can check for problems with preferences and try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.