Their most recent match with a tier 1 side was against France. They lost by 25.
No it was against Wales a week later and they lost 17-13. I also think you can pretty much include Samoa as a tier 1 team and they were very impressive against them in the final of the PNC (Pacific Nations Cup).
Outside of world cups Fiji have a lot less time together at full strength than tier 1 teams. Their preparation for games is almost always poor. But it isn't now. And Fiji's scrum might have been dominated by the French scrum, but so was England's recently. Their scrum matched Japan's in the PNC (Pacific Nations Cup), which had parity with Georgia's last week.
Their props might not be top level players but they aren't bad scrummagers. And outside of their front row they're all top level club players. If Matawalu gets injured they're a bit screwed, and to a lesser extent Matavesi, but with the starters on the field they're quality. Underestimate them at your peril.