While opening multiple (eg. 20-30) pages in Page namespace in separate tabs in Firefox the proofread tools are often (70-80%) absent from toolbar. Reloading the page does not fix the problem.
Everything works fine with the old toolbar.
Proofread tools are critical for Wikisource project.
I noticed also, that the new toolbar make FF 30-40% higher memory consuming. Unsure if it does matter.