Percentages are rarely informative without an absolute reference.
A 5% raise for someone who makes $20k per year is $1k, whereas a 5% raise for someone who makes $200k is $10k, which would be a 50% raise for the former.
You've demonstrated you understand how to use the score to compare both inter-browser performance (analogous to the amount each makes per year) as well as individual browser performance improvements (analogous to the amount of the raise). Seems pretty informative to me?