For a comparative view on RNA-Seq data from different conditions we use the Integrated Genome Browser (IGB) currently. To do so we translate the read mapping output to GR files - a very lightweight format with two columns: one for the position of a nucleotide, one for the coverage value of it. The advantage of this approach is that the coverage values can be normalized during the GR-file creation (e.g. to the number of mapped reads of each probe) which makes a comparison of different samples possible.
The problem is that the IGB is rather slow so I would like to know if there is any other genome browser that can either handle the mentioned GR files or is able to normalize/rescale the shown coverages. It should be quicker than IGB (to load and to handle - I guess this kills most of the web based genome browsers like GBrowse/GBrowse2) and open-source licensed.
Can anyone suggest a genome browser which fulfills the admittedly long wish list?
PS: I am aware of the similar question but my precise problem is not covered there.