It's with Firefox, right?
Most certificate-related problems in Firefox can be solved by installing a user certificate. To do so, go to Menu → Settings → Network → HTTPS Filtering → Install certificate to Firefox. Note that in release version of Firefox this is only possible on rooted devices. In beta and nightly versions of Firefox this method will work on any device.
Problems with certificate in an app
If any app displays certificate-related errors, disable HTTPS filtering for that app in Menu → Apps Management. After that contact support (Menu → Support → Send Feedback) — we might be able to find a better solution.