Its a simple addon that will let you select which tabs you want to restore on a general startup, just like after a crash, using a similar page to the "Well, this is embarrassing." one. In order to work, you must set the "Options/General/When firefox starts" option to "Show my windows and tabs from last time".
Credit for the idea: the DtTvB
2014-05-19: as of firefox 29 it doesnt seem to work. This addon is a lightweight hack that always shows a modified version of the "Well, this is embarassing" page, but it seems to have been removed from firefox (at least i havent seen it after crashes in a while). As mozilla keeps removing all the features i like about this browser and replacing them with increasing number of crashes, i will not develop this addon any further.