In a desperate attempt to reduce the load on my system when running Firefox 3 with 20+ tabs open (and to try out the newest incarnation of this great browser), I decided to try out Firefox 3.5. This how-to from web upd8 shows the installation procedure using a semi-official PPA mirror (so the builds is hopefully updated quite often).
It seems that the browser speed has increased. Page rendering is almost the same as in Firefox 3, though I have noted a difference in Google Reader when switching categories using hotkeys (it looks as though the shadow text is replicated). The new tab:next integration (install it if using FF 3.5!) shows great potential for the browser and is quite usable.