Installed to a 7.0 32-bit machine that had not had esr before. Did not manually remove the existing ff 28.0. Only had time to start it, watch it "checking to see if your plugins are compatible . . .", grab the user's homepage (duckduckgo lite), then open the forum in a new tab. All that went well. Of course, there were two "firefox" entires in the DE's menu. Not sure whether that should be changed at all. Could get sticky, what with "default browser" and all.
Installed to my own 7.0 32-bit, which by now had Firefox-esr 24.5 as the only Firefox left. Upgrading that to the new 24.6.0-esr with slapt-get went fine. One Firefox menu entry, and it seems to run well.
For 7.0, might consider moving this to non-purged area of repo NOW. Could be wrong (see other posts), but I think 19.0 is the latest installable Firefox in there.